3D semiconductor device and structure

ABSTRACT

A 3D semiconductor device including: a first level including a first layer, the first layer including first transistors, and where the first level includes a second layer, the second layer including first interconnections; a second level overlaying the first level, where the second level includes a third layer, the third layer including second transistors, where the second level includes a fourth layer, the fourth layer including second interconnections; and a plurality of connection paths, where the plurality of connection paths provides connections from a plurality of the first transistors to a plurality of the second transistors, where the second level is bonded to the first level, where the bonded includes oxide to oxide bond regions, where the bonded includes metal to metal bond regions, where the second level includes at least one memory array, where the third layer includes crystalline silicon, where the second layer includes radio frequency type circuits.

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/482,787 filed on Apr. 9, 2017 which is acontinuation-in-part of U.S. patent application Ser. No. 14/607,077filed on Jan. 28, 2015 (now U.S. Pat. No. 9,640,531, issued on May 2,2017); which claims benefit of provisional U.S. Patent Application No.62/042,229, filed on Aug. 26, 2014, provisional U.S. Patent ApplicationNo. 62/035,565, filed on Aug. 11, 2014, provisional U.S. PatentApplication No. 62/022,498, filed on Jul. 9, 2014, and provisional U.S.Patent Application No. 61/932,617, filed on Jan. 28, 2014. U.S. patentapplication Ser. No. 14/607,077 is also a continuation-in-part of U.S.patent application Ser. No. 14/628,231 filed on Feb. 21, 2015 (now U.S.Pat. No. 9,142,553, issued on Sep. 22, 2015) The entire contents of theforegoing applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates to the general field of Integrated Circuit (IC)devices and fabrication methods, and more particularly to multilayer orThree Dimensional Integrated Circuit (3D-IC) devices and fabricationmethods.

2. Discussion of Background Art

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplementaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate the performance, functionality and powerconsumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of        transistors (with or without wiring levels) can be constructed        separately. Following this, they can be bonded to each other and        connected to each other with through-silicon vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318; and pending U.S. patent        application Publications and application Ser. Nos. 14/642,724,        15/150,395, 15/173,686, 62/651,722; 62/681,249, 62/713,345,        62/770,751, 62/952,222, 2020/0013791, 16/558,304; and PCT        Applications (and Publications): PCT/US2010/052093,        PCT/US2011/042071 (WO2012/015550), PCT/US2016/52726        (WO2017053329), PCT/US2017/052359 (WO2018/071143),        PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332 (WO        2019/060798). The entire contents of the foregoing patents,        publications, and applications are incorporated herein by        reference.

Electro-Optics: There is also work done for integrated monolithic 3Dincluding layers of different crystals, such as U.S. Pat. Nos.8,283,215, 8,163,581, 8,753,913, 8,823,122, 9,197,804, 9,419,031,9,941,319, and 10,679,977. The entire contents of the foregoing patents,publications, and applications are incorporated herein by reference.

An early work on monolithic 3D was presented in U.S. Pat. No. 7,052,941and follow-on work in related patents includes U.S. Pat. No. 7,470,598.A technique which has been used over the last 20 years to build SOIwafers, called “Smart-Cut” or “Ion-Cut”, was presented in U.S. Pat. No.7,470,598 as one of the options to perform layer transfer for theformation of a monolithic 3D device. Yet in a related patent disclosure,by the same inventor of U.S. Pat. No. 7,470,598, U.S. application Ser.No. 12/618,542 it states: “In one embodiment of the previous art,exfoliating implant method in which ion-implanting Hydrogen into thewafer surface is known. But this exfoliating implant method can destroylattice structure of the doped layer 400 by heavy ion-implanting. Inthis case, to recover the destroyed lattice structure, a long timethermal treatment in very high temperature is required. This longtime/high temperature thermal treatment can severely deform the celldevices of the lower region.” Moreover, in U.S. application Ser. No.12/635,496 by the same inventor is stated:

Among the technologies to form the detaching layer, one of the wellknown technologies is Hydrogen Exfoliating Implant. This method has acritical disadvantage which can destroy lattice structures of thesubstrate because it uses high amount of ion implantation. In order torecover the destroyed lattice structures, the substrate should be curedby heat treatment in very high temperature long time. This kind of hightemperature heat treatment can damage cell devices in the lowerregions.” Furthermore, in U.S. application Ser. No. 13/175,652 it isstated: “Among the technologies to form the detaching layer 207, onetechnology is called as exfoliating implant in which gas phase ions suchas hydrogen is implanted to form the detaching layer, but in thistechnology, the crystal lattice structure of the multiple doped layers201, 203, 205 can be damaged. In order to recover the crystal latticedamage, a thermal treatment under very high temperature and longtimeshould be performed, and this can strongly damage the cell devicesunderneath.” In fact the Inventor had posted a video infomercial on hiscorporate website, and was up-loaded on YouTube on Jun. 1, 2011, clearlystating in reference to the Smart Cut process: “The wafer bonding anddetaching method is well-known SOI or Semiconductor-On-Insulatortechnology. Compared to conventional bulk semiconductor substrates, SOIhas been introduced to increase transistor performance. However, it isnot designed for 3D IC either. Let me explain the reasons . . . . Thedose of hydrogen is too high and, therefore, semiconductor crystallinelattices are demolished by the hydrogen ion bombardment during thehydrogen ion implantation. Therefore, typically annealing at more than1,100 Celsius is required for curing the lattice damage after waferdetaching. Such high temperature processing certainly destroysunderlying devices and interconnect layers. Without high temperatureannealing, the transferred layer should be the same as a highlydefective amorphous layer. It seems that there is no way to cure thelattice damage at low temperatures. BeSang has disruptive 3D layerformation technology and it enables formation of defect-free singlecrystalline semiconductor layer at low temperatures . . . .”

In at least one embodiment presented herein, at least one innovativemethod and device structure to repair the crystal lattice damage causedby the hydrogen implant is described.

Regardless of the technique used to construct 3D stacked integratedcircuits or chips, heat removal is a serious issue for this technology.For example, when a layer of circuits with power density P is stackedatop another layer with power density P, the net power density is 2P.Removing the heat produced due to this power density is a significantchallenge. In addition, many heat producing regions in 3D stackedintegrated circuits or chips have a high thermal resistance to the heatsink, and this makes heat removal even more difficult.

Several solutions have been proposed to tackle this issue of heatremoval in 3D stacked integrated circuits and chips. These are describedin the following paragraphs.

Publications have suggested passing liquid coolant through multipledevice layers of a 3D-IC to remove heat. This is described in“Microchannel Cooled 3D Integrated Systems”, Proc. Intl. InterconnectTechnology Conference, 2008 by D. C. Sekar, et al., and “ForcedConvective Interlayer Cooling in Vertically Integrated Packages,” Proc.Intersoc. Conference on Thermal Management (ITHERM), 2008 by T.Brunschweiler, et al.

Thermal vias have been suggested as techniques to transfer heat fromstacked device layers to the heat sink. Use of power and ground vias forthermal conduction in 3D-ICs has also been suggested. These techniquesare described in “Allocating Power Ground Vias in 3D ICs forSimultaneous Power and Thermal Integrity” ACM Transactions on DesignAutomation of Electronic Systems (TODAES), May 2009 by Hao Yu, Joanna Hoand Lei He.

In addition, thermal limitations during IC fabrication have been a bigobstacle on the road to monolithic three-dimensional ICs. Thesemiconductor and microelectronic processing techniques to formtransistors, circuits, and devices, for example to form some siliconoxides or nitrides, repair damages from processes such as etching andion-implantation, annealing and activation of ion implanted species, andepitaxial regrow techniques, have processing temperatures (for example,greater than 400° C.) and times at temperature that would damage andharm the underlying metallization and/or device layers and structures.These processes may involve transient (short timescales, such as lessthan 500 ns short wavelength laser pulses) heat exposures to the waferbeing processed, or steady state applications (such as RTA, RTO, spike,flash, CVD, ALD) of heat and/or heated material or gases that may haveprocessing times of seconds, minutes, or hours.

Techniques to remove heat from 3D Integrated Circuits and Chips andprotect sensitive metallization and circuit elements from either theheat of processing of the 3D layers or the operationally generated heatfrom an active circuit, will be beneficial.

Additionally the 3D technology according to some embodiments of theinvention may enable some very innovative IC devices alternatives withreduced development costs, novel and simpler process flows, increasedyield, and other illustrative benefits.

SUMMARY

The invention may be directed to multilayer or Three DimensionalIntegrated Circuit (3D IC) devices and fabrication methods.

In one aspect, a 3D semiconductor device, the device comprising: a firstlevel, wherein said first level comprises a first layer, said firstlayer comprising first transistors, and wherein said first levelcomprises a second layer, said second layer comprising firstinterconnections; a second level overlaying said first level, whereinsaid second level comprises a third layer, said third layer comprisingsecond transistors, and wherein said second level comprises a fourthlayer, said fourth layer comprising second interconnections; and aplurality of connection paths, wherein said plurality of connectionpaths provides connections from a plurality of said first transistors toa plurality of said second transistors, wherein said second level isbonded to said first level, wherein said bonded comprises oxide to oxidebond regions, wherein said bonded comprises metal to metal bond regions,wherein said third layer comprises crystalline silicon, wherein saidsecond level comprise electronic circuits and at least one test circuit,and wherein said at least one test circuit is capable to perform testingof at least one of said electronic circuits.

In another aspect, a 3D semiconductor device, the device comprising: afirst level, wherein said first level comprises a first layer, saidfirst layer comprising first transistors, and wherein said first levelcomprises a second layer, said second layer comprising firstinterconnections; a second level overlaying said first level, whereinsaid second level comprises a third layer, said third layer comprisingsecond transistors, and wherein said second level comprises a fourthlayer, said fourth layer comprising second interconnections; a pluralityof connection paths, wherein said plurality of connection paths providesconnections from a plurality of said first transistors to a plurality ofsaid second transistors, wherein said second level is bonded to saidfirst level, wherein said bonded comprises oxide to oxide bond regions,wherein said bonded comprises metal to metal bond regions, wherein saidthird layer comprises crystalline silicon, wherein said second levelcomprises at least one array of memory cells, wherein said memory cellsare volatile type memory cells, and wherein each of said memory cellsare a single transistor memory cell.

In another aspect, a 3D semiconductor device, the device comprising: afirst level, wherein said first level comprises a first layer, saidfirst layer comprising first transistors, and wherein said first levelcomprises a second layer, said second layer comprising firstinterconnections; a second level overlaying said first level, whereinsaid second level comprises a third layer, said third layer comprisingsecond transistors, and wherein said second level comprises a fourthlayer, said fourth layer comprising second interconnections; and aplurality of connection paths, wherein said plurality of connectionpaths provides connections from a plurality of said first transistors toa plurality of said second transistors, wherein said second level isbonded to said first level, wherein said bonded comprises oxide to oxidebond regions, wherein said bonded comprises metal to metal bond regions,wherein said second level comprises at least one memory array, whereinsaid third layer comprises crystalline silicon, and wherein said secondlayer comprises radio frequency (“RF”) type circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIG. 1 is an exemplary illustration of a laser annealing machine'soutput that may form a large rectangular window of uniform laser energy;

FIGS. 2A-2B are exemplary drawing illustrations of a process flow formanufacturing a crystallized layer suitable for forming transistors;

FIG. 3 is an exemplary illustration of a layered shield/heat sink layerthat may be constructed wherein the horizontal heat conductivity or heatspreading capability may be substantially greater in the horizontaldirection than in the vertical direction;

FIG. 4 is an exemplary illustration of a partially processed 3D devicewith substrate being processed with topside illumination and includingthermally conductive paths;

FIGS. 5A-5F are exemplary drawing illustrations of an additional processflow for manufacturing fully depleted MOSFET (FD-MOSFET) with anintegrated shield/heat sink layer;

FIG. 6 is an exemplary illustration of some additional embodiments andcombinations of devices, circuits, paths, and connections of a 3Ddevice;

FIG. 7 is an exemplary illustration of a 3D platform;

FIG. 8 is an exemplary illustration of a cross-section picture of adevice that includes trench capacitors;

FIG. 9 is an exemplary illustration of a 3D device power distributionstructure;

FIG. 10 is an exemplary illustration of a flowchart of a system thatuses a processor and at least one bus;

FIG. 11A illustrates an exemplary partitioned 3D system/device;

FIG. 11B is an exemplary illustration of a flowchart of partitioninglogic units onto at least two stratums;

FIG. 12A is an exemplary illustration of different Clock distributionnetwork styles;

FIGS. 12B and 12C illustrate exemplary 3D system/device clockdistribution networks;

FIGS. 13A-13G are exemplary illustrations of an n-channel FD-MOSFET withintegrated TRL (Trap Rich Layer) device and process flow;

FIGS. 14A-14E are exemplary illustrations of an additional n-channelFD-MOSFET with integrated TRL (Trap Rich Layer) device and process flow;

FIGS. 15A-15G are exemplary illustrations of a MEMS oscillatorintegrated in a 3DIC stack system and process flow;

FIGS. 16A-16K are exemplary illustrations of 3DIC process flow withcarrier wafer;

FIG. 17 is an exemplary illustration of a stratum-3 and a stratum-2 in adual strata configuration overlaying a target/base wafer or device;

FIG. 18A is an exemplary illustration of back to back memory cells in astratum-3 and a stratum-2 in a dual strata configuration utilizing aunified back-bias;

FIG. 18B is an exemplary illustration of N-channel and P-channeltransistors each in a stratum-3 and a stratum-2 with its own back biasor a shared back-bias in a dual strata configuration;

FIG. 18C is an exemplary illustration of Finfet transistors each in astratum-3 and a stratum-2 in a dual strata configuration;

FIG. 18D is an exemplary illustration of four doping-layer transistorstructures in a stratum-3 and a stratum-2 in a dual strataconfiguration;

FIGS. 19A-19K are exemplary illustrations of a process flow for theformation of stratum-2 and stratum-3 devices (thus forming a dualstrata), which may be layer transferred and connected to a targetwafer/substrate;

FIG. 20 is an exemplary illustration of a 3DIC device; and

FIG. 21 is an exemplary illustration of a 3DIC device formation flowutilizing a detachable donor substrate and a detachable carriersubstrate.

DETAILED DESCRIPTION

An embodiment of the invention is now described with reference to thedrawing figures. Persons of ordinary skill in the art will appreciatethat the description and figures illustrate rather than limit theinvention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by the appended claims.

Some drawing figures may describe process flows for building devices.The process flows, which may be a sequence of steps for building adevice, may have many structures, numerals and labels that may be commonbetween two or more adjacent steps. In such cases, some labels, numeralsand structures used for a certain step's figure may have been describedin the previous steps' figures.

Some monolithic 3D approaches are described in U.S. Pat. Nos. 8,273,610,8,557,632, 8,298,875, 8,557,632, 8,163,581, 8,378,715, 8,379,458,8,450,804, 8,574,929, 8,581,349, 8,687,399, 8,742,476, 8,674,470; USpatent publication 2013/0020707; and pending U.S. patent applicationSer. Nos. 13/803,437, 14/298,917, 61/932,617, 62/042,229 and 13/796,930.The contents of the foregoing patents, publications, and applicationsare incorporated herein by reference.

Defect annealing, such as furnace thermal or optical annealing, of thinlayers of the crystalline materials generally included in 3D-ICs to thetemperatures that may lead to substantial dopant activation or defectanneal, for example above 600° C., may damage or melt the underlyingmetal interconnect layers of the stacked 3D-IC, such as copper oraluminum interconnect layers. An embodiment of the invention is to form3D-IC structures and devices wherein a heat spreading, heat conductingand/or optically reflecting or absorbent material layer or layers (whichmay be called a shield) is incorporated between the sensitive metalinterconnect layers and the layer or regions being optically irradiatedand annealed, or annealed from the top of the 3D-IC stack using othermethods. An exemplary generalized process flow is shown in FIGS. 33A-Fof incorporated U.S. Pat. No. 8,574,929. An exemplary process flow foran FD-RCAT with an optional integrated heat shield/spreader is shown inFIGS. 34A-G of incorporated U.S. Pat. No. 8,574,929. An exemplaryprocess flow for a FD-MOSFET with an optional integrated heatshield/spreader is shown in FIGS. 45A-G of incorporated U.S. Pat. No.8,574,929. An exemplary process flow for a planar fully depletedn-channel MOSFET (FD-MOSFET) with an optional integrated heatshield/spreader and back planes and body bias taps is shown in FIGS.46A-G of incorporated U.S. Pat. No. 8,574,929. An exemplary process flowfor a horizontally oriented JFET or JLT with an optional integrated heatshield/spreader is shown in FIGS. 47A-G of incorporated U.S. Pat. No.8,574,929. An alternate method to construct a planar fully depletedundoped channel MOSFET (FD-MOSFET) with an optional integrated heatshield/spreader and back planes and body bias taps suitable for amonolithic 3D IC is shown in FIGS. 5A-5F herein. The 3D-ICs may beconstructed in a 3D stacked layer using procedures outlined herein andsuch as, for example, FIGS. 39, 40, 41 of incorporated U.S. Pat. No.8,574,929 and in other incorporated references. The topside defectanneal may include optical annealing to repair defects in thecrystalline 3D-IC layers and regions (which may be caused by the ion-cutimplantation process), and may be utilized to activate semiconductordopants in the crystalline layers or regions of a 3D-IC, such as, forexample, LDD, halo, source/drain implants. The 3D-IC may include, forexample, stacks formed in a monolithic manner with thin layers or stacksand vertical connection such as TLVs, and stacks formed in an assemblymanner with thick (>2 um) layers or stacks and vertical connections suchas TSVs. Optical annealing beams or systems, such as, for example, alaser-spike anneal beam from a commercial semiconductor materialoriented single or dual-beam continuous wave (CW) laser spike annealDB-LSA system of Ultratech Inc., San Jose, Calif., USA (10.6 um laserwavelength), or a short pulse laser (such as 160 ns), with 308 nmwavelength, and large area (die or step-field sized, including 1 cm²)irradiation such as offered by Excico of Gennevilliers, France, may beutilized (for example, see Huet, K., “Ultra Low Thermal Budget LaserThermal Annealing for 3D Semiconductor and Photovoltaic Applications,”NCCAVS 2012 Junction Technology Group, Semicon West, San Francisco, Jul.12, 2012). Additionally, the defect anneal may include, for example,laser anneals (such as suggested in Rajendran, B., “Sequential 3D ICFabrication: Challenges and Prospects”, Proceedings of VLSI Multi LevelInterconnect Conference 2006, pp. 57-64), Ultrasound Treatments (UST),megasonic treatments, and/or microwave treatments. The topside defectanneal ambient may include, for example, vacuum, high pressure (greaterthan about 760 torr), oxidizing atmospheres (such as oxygen or partialpressure oxygen), and/or neutral/reducing atmospheres (such as nitrogenor argon or hydrogen). The topside defect anneal may includetemperatures of the layer being annealed above about 400° C. (a hightemperature thermal anneal), including, for example, 600° C., 800° C.,900° C., 1000° C., 1050° C., 1100° C. and/or 1120° C., and the sensitivemetal interconnect (for example, may be copper or aluminum containing)and/or device layers below may not be damaged by the annealing process,for example, which may include sustained temperatures that do not exceed200° C., exceed 300° C., exceed 370° C., or exceed 400° C. As understoodby those of ordinary skill in the art, short-timescale (nanosceonds tomiliseconds) temperatures above 400° C. may also be acceptable fordamage avoidance, depending on the acceptor layer interconnect metalsystems used. The topside defect anneal may include activation ofsemiconductor dopants, such as, for example, ion implanted dopants orPLAD applied dopants. It will also be understood by one of ordinaryskill in the art that the methods, such as the heat sink/shield layerand/or use of short pulse and short wavelength optical anneals, mayallow almost any type of transistor, for example, such as FinFets,bipolar, nanowire transistors, to be constructed in a monolithic 3Dfashion as the thermal limit of damage to the underlying metalinterconnect systems is overcome. Moreover, multiple pulses of thelaser, other optical annealing techniques, or other anneal treatmentssuch as microwave, may be utilized to improve the anneal, activation,and yield of the process. The transistors formed as described herein mayinclude many types of materials; for example, the channel and/or sourceand drain may include single crystal materials such as silicon,germanium, or compound semiconductors such as GaAs, InP, GaN, SiGe, andalthough the structures may be doped with the tailored dopants andconcentrations, they may still be substantially crystalline ormono-crystalline. The transistors in a first layer of transistors mayinclude a substantially different channel and/or source/drain materialthan the second layer of transistors. For example, the first layer oftransistors may include silicon-based transistor channels and the secondlayer of transistors may include a germanium based transistor channels.

One compelling advantage of the Excico's laser annealing machine is itsoutput optical system. This optical system forms a large rectangularwindow of uniform laser energy with less than 10% variation over thesurface to be annealed, and with sharp edges of less than 100 micronbetween the uniform energy and almost no energy as illustrated inFIG. 1. Accordingly a whole die or even reticle could be exposed in oneshot. By setting the window size and aligning the laser to the waferproperly, it could allow the laser annealing process to have thestitching of optical energy, such as pulsed laser exposures, at adesired area, such as the scribe street, such as for example lines 104,potential dicing line 104-1, potential dicing lines 104-2, in FIG. 10 ofincorporated patent reference U.S. Pat. No. 8,273,610 to Or-Bach, et al.Thus, the laser stich may be placed between dies, thereby reducing therisk from uneven exposure at the stitching area affecting any of thedesired circuit transistors or elements. Additionally, the window sizemay be set to cover a multiplicity of dice or tiles, such as end-device3611 of FIG. 36 of incorporated patent reference U.S. Pat. No. 8,273,610to Or-Bach, et al., which may also have potential dice lines, such aspotential dice lines 3602 and/or actual dice lines, such as actual dicelines 3612. The optical annealing could be done sequentially across thewafer or in steppings that substantially cover the entire wafer area butspread the heat generation/absorption to allow better heat dissipationand removal. Such spreading of heat generation could be done, forexample, by scanning the wafer surface like a checkerboard, firstexposing rectangles or areas such as the blacks' of the checkerboard,and then the ‘white’ locations.

Various methods and procedures to form Finfet transistors andthin-side-up transistors, many as part of a 3D stacked layer formation,are outlined herein and in at least U.S. Pat. No. 8,273,610 (at least inFIGS. 58, 146, 220 and associated specification paragraphs), U.S. Pat.Nos. 8,557,632 and 8,581,349, and US Patent Application Publication2013/0020707, and US Patent Applications such as 62/042,229 of theincorporated references.

While concepts in this document have been described with respect to3D-ICs with two stacked device layers, those of ordinary skill in theart will appreciate that it can be valid for 3D-ICs with more than twostacked device layers. Additionally, some of the concepts may be appliedto 2D ICs.

The damage of the to be transferred crystalline layer caused by theion-cut implantation traversing the layer may be thermally annealed, asdescribed in at least FIG. 44 and associated specification ofincorporated U.S. Pat. No. 8,574,929, or may be optically annealed, asdescribed in at least FIGS. 33, 34, 45, 46 and 47 and associatedspecification of incorporated U.S. Pat. No. 8,574,929, or may beannealed by other methods such as ultrasonic or megasonic energy, asdescribed in incorporated U.S. Pat. Nos. 8,574,929, 8,273,610 and8,557,632. These techniques repair the ion-implantation and layertransfer damage that is within the transferred crystalline layer orlayers. An embodiment of the invention is to perform the layer transferof the ion-cut crystalline silicon layer, clean the surface of thetransferred crystalline layer, then deposit a thin layer of amorphoussilicon, and utilize optical annealing to form a layer or layer ofsubstantially monocrystalline silicon in which the devices may be madewith high quality, or the crystalized a-Si layer may be utilized as araised source drain of high dopant concentration. The use of layertransfer techniques that do not use an ion-cut, and hence avoid thedamage issues, are disclosed later herein.

As illustrated in FIG. 2A, an doped or undoped substrate donor wafer 200may be processed to in preparation for layer transfer by ion-cut of alayer of monocrystalline silicon. The structure may include a wafersized layer of doping across the wafer, N-doped layer 202. The N− dopedlayer 202 may be formed by ion implantation and thermal anneal asdescribed elsewhere in the incorporated references and may include acrystalline material, for example, mono-crystalline (single crystal)silicon. N− doped layer 202 may be very lightly doped (less than 1e15atoms/cm³) or lightly doped (less than 1e16 atoms/cm³) or nominallyun-doped (less than 1e14 atoms/cm³). N− doped layer 202 may haveadditional ion implantation and anneal processing to provide a differentdopant level than N− substrate donor wafer 200 and may have graded orvarious layers of doping concentration. The layer stack mayalternatively be formed by epitaxially deposited doped or undopedsilicon layers, or by a combination of epitaxy and implantation, or bylayer transfer. Annealing of implants and doping may include, forexample, conductive/inductive thermal, optical annealing techniques ortypes of Rapid Thermal Anneal (RTA or spike). The top surface of N−substrate donor wafer 200 layer stack may be prepared for oxide waferbonding with a deposition of an oxide or by thermal oxidation of N−doped layer 202 to form oxide layer 280. A layer transfer demarcationplane (shown as dashed line) 299 may be formed by hydrogen implantationor other methods as described in the incorporated references. The N−substrate donor wafer 200, such as surface 282, and acceptor wafer 210may be prepared for wafer bonding as previously described and lowtemperature (less than approximately 400° C.) bonded. Acceptor wafer210, as described herein and in the incorporated references, mayinclude, for example, transistors, circuitry, and metal, such as, forexample, aluminum or copper, interconnect wiring, a metal shield/heatsink layer or layers, and thru layer via metal interconnect strips orpads. Acceptor wafer 210 may be substantially comprised of a crystallinematerial, for example mono-crystalline silicon or germanium, or may bean engineered substrate/wafer such as, for example, an SOI (Silicon onInsulator) wafer or GeOI (Germanium on Insulator) substrate. Acceptorwafer 210 may include transistors such as, for example, MOSFETS,FD-MOSFETS, FinFets, FD-RCATs, BJTs, HEMTs, and/or HBTs. The portion ofthe N− doped layer 202 and the N− substrate donor wafer 200 that may beabove (when the layer stack is flipped over and bonded to the acceptorwafer 210) the layer transfer demarcation plane 299 may be removed bycleaving or other low temperature processes as described in theincorporated references, such as, for example, ion-cut with mechanicalor thermal cleave, thus forming remaining N− layer 203.

As illustrated in FIG. 2B, oxide layer 280 and remaining N− layer 203have been layer transferred to acceptor wafer 210. The top surface ofremaining N− layer 203 may be chemically or mechanically polished,and/or may be thinned by low temperature oxidation and strip processes,such as the TEL SPA tool radical oxidation and HF:H₂O solutions asdescribed herein and in referenced patents and patent applications. Thruthe processing, the wafer sized layer remaining N− layer 203 could bethinned from its original total thickness, and its final total thicknesscould be in the range of about 3 nm to about 30 nm, for example, about 3nm, about 5 nm, about 7 nm, about 10 nm, about 15 nm, about 20 nm, orabout 30 nm. Remaining N− layer 203 may have a thickness that may allowfull gate control of channel operation when the transistor, for examplea JFET (or JLT) or FD-MOSFET, is substantially completely formed.Acceptor wafer 210 may include one or more (two are shown in thisexample) shield/heat sink layers 288, which may include materials suchas, for example, Aluminum, Tungsten (a refractory metal), Copper,silicon or cobalt based silicides, or forms of carbon such as carbonnanotubes, and may be layered itself as described herein FIG. 3. Eachshield/heat sink layer 288 may have a thickness range of about 50 nm toabout 1 mm, for example, about 50 nm, about 100 nm, about 200 nm, about300 nm, about 500 nm, about 0.1 um, about 1 um, about 2 um, and about 10um. Shield/heat sink layer 288 may include isolation openings 287, andalignment mark openings (not shown), which may be utilized for shortwavelength alignment of top layer (donor) processing to the acceptorwafer alignment marks (not shown). Shield/heat sink layer 288 mayinclude one or more shield path connects 285 and shield path vias 283.Shield path via 283 may thermally and/or electrically couple and connectshield path connect 285 to acceptor wafer 210 interconnect metallizationlayers such as, for example, exemplary acceptor metal interconnect 281(shown). Shield path connect 285 may also thermally and/or electricallycouple and connect each shield/heat sink layer 288 to the other and toacceptor wafer 210 interconnect metallization layers such as, forexample, acceptor metal interconnect 281, thereby creating a heatconduction path from the shield/heat sink layer 288 to the acceptorsubstrate 295, and a heat sink (not shown, see incorp. Refs.). Isolationopenings 287 may include dielectric materials, similar to those of BEOLisolation 296. Acceptor wafer 210 may include first (acceptor) layermetal interconnect 291, acceptor wafer transistors and devices 293, andacceptor substrate 295. After cleaning the top surface of remaining N−layer 203, a layer of amorphous silicon 266 may be deposited. Amorphoussilicon layer 266 may have a thickness that could be in the range ofabout 3 nm to about 300 nm, for example, about 3 nm, about 5 nm, about 7nm, about 10 nm, about 15 nm, about 20 nm, about 30 nm, about 50 nm,about 100 nm, about 200 nm or about 300 nm. Using the single crystalnature of remaining N− layer 203, amorphous silicon layer 266 may becrystallized in an epitaxial fashion by exposure to an optical beam, forexample, to short wavelength pulse lasers as described elsewhere hereinand in incorporated references. Amorphous silicon layer 266 may be dopedin-situ during deposition, or may be ion-implanted after deposition anddopants activated during the optical exposure. Further, amorphoussilicon layer 266 may be first crystalized and then ion-implanted withdopants, and then those dopants may be activated with an additionalanneal, for example, an optical beam anneal. Optical anneal beams, suchas exemplary crystallization/annealing ray 265, may be optimized tofocus light absorption and heat generation within or at the surface ofamorphous silicon layer 266 to promote the epitaxial regrow into a layerof doped single crystal silicon. The laser assistedcrystallization/annealing with the absorbed heat generated by exemplarycrystallization/annealing ray 265 may also include a pre-heat of thebonded stack to, for example, about 100° C. to about 400° C., and/or arapid thermal spike to temperatures above about 200° C. to about 600° C.Additionally, absorber layers or regions, for example, includingamorphous carbon, amorphous silicon, and phase changing materials (seeU.S. Pat. Nos. 6,635,588 and 6,479,821 to Hawryluk et al. for example),may be utilized to increase the efficiency of the optical energy capturein conversion to heat for the desired annealing or activation processes.Moreover, multiple pulses of the laser may be utilized to improve theanneal, activation, and yield of the process. Reflected ray 263 may bereflected and/or absorbed by shield/heat sink layer 288 regions thusblocking the optical absorption of ray blocked metal interconnect 281.Heat generated by absorbed photons from, for example,crystallization/annealing ray 265 may also be absorbed by shield/heatsink layer 288 regions and dissipated laterally and may keep thetemperature of underlying metal layers, such as metal interconnect 281,and other metal layers below it, cooler and prevent damage. Shield/heatsink layer 288 and associated dielectrics may laterally spread andconduct the heat generated by the topside defect anneal, and inconjunction with the dielectric materials (low heat conductivity) aboveand below shield/heat sink layer 288, keep the interconnect metals andlow-k dielectrics of the acceptor wafer interconnect layers cooler thana damage temperature, such as, for example, 400° C. or 370° C., or 300°C. A second layer of shield/heat sink layer 288 may be constructed(shown) with a low heat conductive material sandwiched between the twoheat sink layers, such as silicon oxide or carbon doped ‘low-k’ siliconoxides, for improved thermal protection of the acceptor waferinterconnect layers, metal and dielectrics. Shield/heat sink layer 288may act as a heat spreader and/or absorber. Electrically conductivematerials may be used for the two layers of shield/heat sink layer 288and thus may provide, for example, a Vss and a Vdd plane and/or gridthat may be connected to the donor layer transistors above, as well maybe connected to the acceptor wafer transistors below, and/or may providebelow transferred layer device interconnection. Shield/heat sink layer288 may include materials with a high thermal conductivity greater than10 W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237W/m-K), Tungsten (about 173 W/m-K), Plasma Enhanced Chemical VaporDeposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and ChemicalVapor Deposited (CVD) graphene (about 5000 W/m-K). Shield/heat sinklayer 288 may be sandwiched and/or substantially enclosed by materialswith a low thermal conductivity (less than 10 W/m-K), for example,silicon dioxide (about 1.4 W/m-K). The sandwiching of high and lowthermal conductivity materials in layers, such as shield/heat sink layer288 and under & overlying dielectric layers, absorbs and/or spreads thelocalized heat/light energy of the topside anneal laterally and protectsthe underlying layers of interconnect metallization & dielectrics, suchas in the acceptor wafer 210, from harmful temperatures or damage. Whenthere may be more than one shield/heat sink layer 288 in the device, theheat conducting layer closest to the second crystalline layer or oxidelayer 280 may be constructed with a different material, for example ahigh melting point material, for example a refractory metal such astungsten, than the other heat conducting layer or layers, which may beconstructed with, for example, a lower melting point material, forexample such as aluminum or copper. Now transistors may be formed withlow effective temperature (less than approximately 400° C. exposure tothe acceptor wafer 210 sensitive layers, such as interconnect and devicelayers) processing, and may be aligned to the acceptor wafer alignmentmarks (not shown) as described in the incorporated references. This mayinclude further optical defect annealing or dopant activation steps. TheN− donor wafer 200 may now also be processed, such as smoothing andannealing, and reused for additional layer transfers. The insulatorlayer, such as deposited bonding oxides (for example oxide layer 280)and/or before bonding preparation existing oxides (for example the BEOLisolation 296 on top of the topmost metal layer of shield/heat sinklayer 288), between the donor wafer transferred monocrystalline layerand the acceptor wafer topmost metal layer, may include thicknesses ofless than about 1 um, less than about 500 nm, less than about 400 nm,less than about 300 nm, less than about 200 nm, or less than about 100nm. Transistors and other devices, such as those described herein and inincorporated referenced patents and patent applications, may beconstructed utilizing regions of the crystallized amorphous siliconlayer 266 as a portions of the transistor or device; for example, as atransistor channel for an FD-MOSFET or JFET, or as raised source anddrain for an FDMOSFET or JLT.

The shield layer, for example, shield/heat sink layer 288 describedherein, could be constructed so it may have a substantially larger orbetter heat conductivity to the sides of the device in the horizontalorientation than the heat conductivity of the shield layer in thevertical direction toward the underlying layers or back to the topsurface of the device. Such shield layer, wherein the horizontal heatconductivity or heat spreading capability is substantially greater inthe horizontal direction than in the vertical direction, could include a‘sandwich’ of heat conductive thin layer, such as a metal (for examplecopper), overlaid by a thin lower-thermally-conducting layer, forexample SiO2, and may repeat the two layer stack multiple times.Vertical electrical continuity may be maintained by etching verticalvias and filling the vias with an electrically conductive material.Overlapping shorting vias or lines may also perform the same function.Such a shield layer could be designed to support various types ofoptical annealing. Such shielding can block even non laser opticalannealing or a CO₂ laser that tends to penetrate very deeply. In somecases it might be desired to have the top layer of the shielding layeras non-reflective or as a defusing reflector to reduce damage to thelaser annealing machine from the reflected light.

As illustrated in FIG. 3, a layered shield/heat sink layer may beconstructed wherein the horizontal heat conductivity or heat spreadingcapability may be substantially greater in the horizontal direction thanin the vertical direction. The horizontal direction is indicated byhorizontal arrow 350 and the vertical direction is indicated by verticalarrow 352. A portion of FIG. 47G of incorporated reference U.S. Pat. No.8,574,929 is repeated in FIG. 3, showing the portion of a 3D device withshield/heat sink & spreading structure below the second crystallinedevice layer, which may include oxide layer 4780, a portion of thrulayer vias (TLVs) 4760, shield path connects 4785, shield path via 4783,BEOL isolation 4796, shield path via 4783, acceptor metal interconnect4781, first (acceptor) layer metal interconnect 4791, acceptor wafertransistors and devices 4793, acceptor substrate 4795, and acceptorwafer heat sink 4797 (which may have an external surface or connectionto one as described earlier herein), of acceptor wafer 4710. Theexternal surface may be at the top, bottom or sides of the finisheddevice. The device may include an external surface from which heattransfer may take place by methods such as air cooling, liquid cooling,or attachment to another heat sink or heat spreader structure. Asindicated in FIG. 3, the area within the circle is blown up to enableclarity of detail for the illustration. Layered shield/heat sink region385 may include layers or regions of heat conductive material and heatisolative material, for example heat conducting regions 370 and heatisolative regions 372. Heat conducting regions 370 may include materialswith a high thermal conductivity greater than 10 W/m-K, such as, forexample, (about 400 W/m-K), aluminum (about 237 W/m-K), Tungsten (about173 W/m-K), Plasma Enhanced Chemical Vapor Deposited Diamond LikeCarbon-PECVD DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD)graphene (about 5000 W/m-K), barrier metals such as TiN and TaN, and maybe deposited in layers interspersed with heat isolative layers. Heatisolative regions 372 may include materials with a low thermalconductivity (less than 10 W/m-K), or substantially less thermallyconductive than the material included in heat conducting regions 370,materials such as, for example, silicon oxide (about 1.4 W/m-K),aerogels, carbon doped oxides. Accordingly, depending on materialchoices and construction (such as number of cond/iso layers and theirthickness), layered shield/heat sink region 385 may have a heatconductivity in the horizontal direction that is 2 times, or 4 times, orten times greater than the heat conductivity in the vertical direction.Either or both of heat conducting regions 370 and heat isolative regions372 may be electrically conductive. Heat conducting regions 370 and heatisolative regions 372 may be formed by lithographically defining andthen etching the conductive and isolative layer stack using subtractiveformation techniques known by those skilled in the art, and may also beformed in a damascene method. Electrical connection between the variousheat conducting regions 370 may be made by forming the deep TLV 360,patterned after thru layer vias (TLVs) 4760, to short the various heatconduction regions 370. Deep TLV 360 may be formed by etchingsubstantially to, within, or thru the bottom heat conducting region 370of layered shield/heat sink region 385. Thus layered shield/heat sinkregion 385 may be formed wherein the horizontal heat conductivity orheat spreading capability may be substantially greater in the horizontaldirection (indicated by horizontal arrow 350) than in the verticaldirection (indicated by vertical arrow 352). Shield path connect 383 maybe similar to shield path connects 4785 and additional shield/heat sinkregion 388 may be layered such as, for example, layered shield/heat sinkregion 385 or shield/heat sink layers 4788 of FIG. 47G of incorporatedreference U.S. Pat. No. 8,574,929. Layered shield/heat sink region 385may be utilized as part of a thermal conduction path, emf shield,back-bias circuits for second layer transistors, and other uses asdescribed herein in relation to FIG. 47 of incorporated reference U.S.Pat. No. 8,574,929, and any other descriptions employing a shield/heatsink layer or region.

Persons of ordinary skill in the art will appreciate that theillustrations in FIG. 3 are exemplary and are not drawn to scale. Suchskilled persons will further appreciate that many variations may bepossible such as, for example, subtractive region formation techniquesmay be preferred over damascene for forming layered shield/heat sinkregion 385 as the shield regions may comprise the majority of the devicearea at that formation step, and CMP processes within the damascenetechniques may be difficult without breaking the shield into smallregions, which may affect the heat shielding capability. Two or morelayered shield/heat sink layers, properly designed and layed out withoverlapping regions, may be useful for the damascene technique.Moreover, when the layered shield/heat sink region 385 is formed by adamascene process flow, then electrical connection between the variousheat conducting regions 370 may be made at the top surface of thedamascene ‘metal’ line trench by just a slight over-etch (CMP smearingmay not be enough to couple the conductive regions) during deep TLV 360formation, as many of the various heat conducting regions 370 and heatisolative regions 372 may truncate at the top surface of the trench thatis forming layered shield/heat sink region 385. Furthermore, deep TLV360 may be formed to be fully or partially on the outside edge of thelayered shield/heat sink region 385 in order to couple the various heatconducting regions 370. Many other modifications within the scope of theillustrated embodiments of the invention will suggest themselves to suchskilled persons after reading this specification. Thus the invention isto be limited only by the appended claims.

An embodiment of the invention may include an exemplary partiallyprocessed 3D device with substrate being processed with topsideillumination as illustrated in FIG. 4. The topside illumination 499 maybe an optical anneal for purposes, such as, for example, dopantannealing, STI densification and annealing, silicidation, and/or ion-cutdamage repair, which have been described herein and in incorporatedpatents and patent publications and applications. Furthermore, topsideillumination 499 may be an optical anneal that is die sized, or reticlesized, or other size and shape as has been described herein and inincorporated patents and patent publications and applications. Atransferred layer 403, which may be a transferred layer or layers asdescribed herein and in incorporated patents and patent publications andapplications, may have been transferred and bonded to an acceptor waferor substrate, and may include bonding at the interface between donorbonding oxide 480 and acceptor bonding oxide 481. Transferred layer 403may have a protect layer 466 (or region) atop it, which may function asa optical absorber, reflector, or energy spreader as described in hereinand in incorporated patents and patent publications and applications,and may remain a part of the device at the end of device processing orbe sacrificial (removed). Transferred layer 403 may include its entiretyor portions, isotopically enriched silicon (such as, for example, >99%²⁸Si) or germanium to enable a greater heat conductivity. The relativelyhigher cost of the isotopically enriched layer or regions can bemitigated by the reuse of a donor wafer comprised wholly or partiallywith the material. The acceptor wafer at the time of bonding to thedonor wafer and at exposure to topside illumination 499 may includeacceptor bonding oxide 481, top shield layer 485, inter-shield insulatorlayer 498, bottom shield layer 488, second inter-shield insulator layer496, eight ‘2×’ interconnect layers 483 that may be interspersed withfour ‘2×’ insulator layers 494, a ‘1×’ interconnect layer 487, a ‘1×’insulator layer 492, device die thermal conduction paths 445, devicescribe-lane thermal conduction paths 446, second device die thermalconduction paths 444, second device scribe-lane thermal conduction paths447, and a base wafer with transistors and circuits 495. The acceptorwafer may have another combination of these layers and regions as wouldbe clear to one skilled in the art. The elements of the exemplaryacceptor wafer may include the materials, process flows, construction,use, etc. as has been described herein and in incorporated patents andpatent publications and applications, for example, transferred layer 403may be doped or undoped silicon, and may have regions of STI or othertransistor elements within it or on it, and may include multiple layersor regions of doping. Moreover, transferred layer 403 may include layersor regions that have materials with melting points higher than 900° C.(for example doped mono-crystalline silicon or polysilicon or amorphoussilicon, tungsten, tantalum nitride) that may be used, for example, as aback-bias or body bias region or layer, as has been described herein andin incorporated patents and patent publications and applications. Topshield layer 485 may have layered shield regions wherein the horizontalthermal conduction is substantially greater than the vertical heatconduction. The bonded stack of the acceptor wafer and transferredlayers may include scribe regions 465; either preformed and/orpredetermined scribelanes and/or dicelines, or may include customfunction definition and etching, or a combination of both. Scriberegions 465 may be constructed with device scribe-lane thermalconduction paths 446 that may provide a thermal conduction path from thetop shield layer 485 to the base wafer with transistors and circuits495, which could then conduct heat that may be generated from topsideillumination 499 to the illumination machine heat sink/chuck 440 andthus help prevent damage from the topside illumination 499 of theacceptor interconnect layers, such as, for example, the eight ‘2×’interconnect layers 483, four ‘2×’ insulator layers 494, 1×′interconnect layer 487, ‘1×’ insulator layer 492, and the transistorsand circuits of base wafer with transistors and circuits 495. Seconddevice scribe-lane thermal conduction paths 447 may thermally conductfrom bottom shield layer 488 to the base wafer with transistors andcircuits 495 and the illumination machine heat sink/chuck 440. Devicedie thermal conduction paths 445 within the device die, may provide athermal conduction path from the top shield layer 485 to the base waferwith transistors and circuits 495, which could then conduct heat thatmay be generated from topside illumination 499 to the illuminationmachine heat sink/chuck 440 and thus help prevent damage from thetopside illumination 499 of the acceptor interconnect layers, such as,for example, the eight ‘2×’ interconnect layers 483, four ‘2×’ insulatorlayers 494, 1×′ interconnect layer 487, ‘1×’ insulator layer 492, andthe transistors and circuits of base wafer with transistors and circuits495, and has been described herein and in incorporated patents andpatent publications. Second device die thermal conduction paths 444 maythermally conduct from bottom shield layer 488 to the base wafer withtransistors and circuits 495 and the illumination machine heatsink/chuck 440. Device scribe-lane thermal conduction paths 446 may beremoved in the later dice singulation processes whereas the device diethermal conduction paths 445 may remain in the finished device andprovide cooling of the second layer and above transistor and circuitlayers when the device is in operation and generating heat from thedevice operation. The density of device die thermal conduction paths445, device scribe-lane thermal conduction paths 446, second device diethermal conduction paths 444, and second device scribe-lane thermalconduction paths 447 is a device design and thermal architecturecalculation, but may be on the order of 1 every 100 um² (Wei H., et al.,“Cooling Three-Dimensional Integrated Circuits Using Power DeliveryNetworks”, IEDM 2012, 14.2, December 2012. incorporated by reference inentirety). Scribelanes (or dicelanes), such as scribe regions 465, maybe about 1 um wide, about 20 um wide, about 50 um wide, about 100 umwide, or greater than about 100 um wide depending on design choice anddie singulation process capability.

Persons of ordinary skill in the art will appreciate that theillustrations in FIG. 4 are exemplary and are not drawn to scale. Suchskilled persons will further appreciate that many variations may bepossible such as, for example, bottom shield layer 488 may also beformed as a layered shield/heat sink layer or region. Moreover, althoughmany of the elements in the FIG. 4 may be called layers, they maininclude within them regions. Furthermore, device scribe-lane thermalconduction paths 446 and device die thermal conduction paths 445 may beformed so that there is no electrical connection to bottom shield layer488, unless they are designed to do so as the same circuit node.Further, the choice of eight ‘2×’ interconnect layers 483 that may beinterspersed with four ‘2×’ insulator layers 494, a ‘1×’ interconnectlayer 487, a ‘1×’ insulator layer 492 is a design choice and may bedifferent according to the design considerations, both devicefunctionally and thermally. Moreover, the various semiconductor layerswithin the 3D device may have various circuitry, functions andconnection, for example, as described herein (such as FIG. 6) or inincorporated patent references. Thus the invention is to be limited onlyby the appended claims.

An alternate method to construct a planar fully depleted undoped channelMOSFET (FD-MOSFET) with an optional integrated heat shield/spreader andback planes and body bias taps suitable for a monolithic 3D IC aspresented in FIG. 46A-46G of incorporated reference U.S. Pat. No.8,574,929 may be constructed as follows. The FD-MOSFET may provide animproved transistor variability control and conduction channelelectrostatic control, as well as the ability to utilize an updopedchannel, thereby improving carrier mobility. In addition, the FD-MOSFETdoes not demand doping or pocket implants in the channel to control theelectrostatic characteristics and tune the threshold voltages.Sub-threshold slope, DIBL, and other short channel effects are greatlyimproved due to the firm gate electrostatic control over the channel. Inthis embodiment, a ground plane is constructed that may provide improvedelectrostatics and/or Vt adjustment and/or back-bias of the FD-MOSFET.In addition, selective regions may be constructed to provide body biasand/or partially depleted/bulk-like transistors. Moreover, a heatspreading, heat conducting and/or optically reflecting material layer orlayers may be incorporated between the sensitive metal interconnectlayers below and the layer or regions being optically irradiated andannealed to repair defects in the crystalline 3D-IC layers and regions,crystallize an undoped transistor channel, and to activate semiconductordopants in the crystalline layers or regions of a 3D-IC without harm tothe sensitive metal interconnect and associated dielectrics. FIGS. 5A-Fillustrate an exemplary undoped-channel FD-MOSFET which may beconstructed in a 3D stacked layer using procedures outlined below and inthe incorporated references.

As illustrated in FIG. 5A, SOI donor wafer substrate 500 may includeback channel layer 502 above Buried Oxide BOX layer 501. Back channellayer 502 may be doped by ion implantation and thermal anneal, mayinclude a crystalline material, for example, mono-crystalline (singlecrystal) silicon and may be heavily doped (greater than 1e16 atoms/cm³),lightly doped (less than 1e16 atoms/cm³) or nominally un-doped (lessthan 1e14 atoms/cm³). SOI donor wafer substrate 500 may include acrystalline material, for example, mono-crystalline (single crystal)silicon and at least the upper layer near BOX layer 501 may be veryheavily doped (greater than 1e20 atoms/cm³). Back channel layer 502 mayhave additional ion implantation and anneal processing to provide adifferent dopant level than SOI donor wafer substrate 500 and may havegraded and/or various layers of doping concentration. SOI donor wafersubstrate 500 may have additional ion implantation and anneal processingto provide a different dopant level than back channel layer 502 and mayhave graded and/or various layers of doping concentration. The layerstack may alternatively be formed by epitaxially deposited doped orundoped silicon layers, or by a combination of epitaxy and implantation,or by layer transfer. Annealing of implants and doping may include, forexample, conductive/inductive thermal, optical annealing techniques ortypes of Rapid Thermal Anneal (RTA or spike). SOI donor wafer may beconstructed by layer transfer techniques described herein or elsewhereas known in the art, or by laser annealed SIMOX at a post donor layertransfer to acceptor wafer step. BOX layer 501 may be thin enough toprovide for effective back and/or body bias, for example, about 25 nm,or about 20 nm, or about 10 nm, or about 35 nm.

As illustrated in FIG. 5B, the top surface of the SOI donor wafersubstrate 500 layer stack may be prepared for oxide wafer bonding with adeposition of an oxide or by thermal oxidation of back channel layer 502to form oxide layer 580. A layer transfer demarcation plane (shown asdashed line) 599 may be formed by hydrogen implantation or other methodsas described in the incorporated references, and may reside within theSOI donor wafer substrate 500. The SOI donor wafer substrate 500 stack,such as surface 582, and acceptor wafer 510 may be prepared for waferbonding as previously described and low temperature (less thanapproximately 400° C.) bonded. Acceptor wafer 510, as described in theincorporated references, may include, for example, transistors,circuitry, and metal, such as, for example, aluminum or copper,interconnect wiring, a metal shield/heat sink layer or layers, and thrulayer via metal interconnect strips or pads. Acceptor wafer 510 may besubstantially comprised of a crystalline material, for examplemono-crystalline silicon or germanium, or may be an engineeredsubstrate/wafer such as, for example, an SOI (Silicon on Insulator)wafer or GeOI (Germanium on Insulator) substrate. Acceptor wafer 510 mayinclude transistors such as, for example, MOSFETS, FD-MOSFETS, FinFets,FD-RCATs, BJTs, HEMTs, and/or HBTs. The portion of the SOI donor wafersubstrate 500 that may be above (when the layer stack is flipped overand bonded to the acceptor wafer 510) the layer transfer demarcationplane 599 may be removed by cleaving or other low temperature processesas described in the incorporated references, such as, for example,ion-cut with mechanical or thermal cleave or other layer transfermethods, thus forming remaining S/D layer 503. Damage/defects tocrystalline structure of back channel layer 502 may be annealed by someof the annealing methods described, for example the short wavelengthpulsed laser techniques, wherein the back channel layer 502 and/orportions of the SOI donor wafer substrate 500 may be heated to defectannealing temperatures, but the layer transfer demarcation plane 599 maybe kept below the temperature for cleaving and/or significant hydrogendiffusion. The optical energy may be deposited in the upper layer of thestack, for example near surface 582, and annealing of back channel layer502 and/or portions of the SOI donor wafer substrate 500 may take placevia heat diffusion. Moreover, multiple pulses of the laser may beutilized to improve the anneal, activation, and yield of the processand/or to control the maximum temperature of various structures in thestack.

As illustrated in FIG. 5C, oxide layer 580, back channel layer 502, BOXlayer 501 and S/D layer 503 may be layer transferred to acceptor wafer510. The top surface of S/D layer 503 may be chemically or mechanicallypolished, and/or may be thinned by low temperature oxidation and stripprocesses, such as the TEL SPA tool radical oxidation and HF:H₂Osolutions as described in referenced patents and patent applications.Thru the processing, the wafer sized layer S/D layer 503 could bethinned from its original total thickness, and its final total thicknesscould be in the range of about 5 nm to about 20 nm, for example, about 5nm, about 7 nm, about 10 nm, about 12 nm, about 15 nm, or about 20 nm.S/D layer 503 may have a thickness and/or doping that may allow aminimum Rext and maximum electron injection velocities when theFD-MOSFET transistor is substantially completely formed. Acceptor wafer510 may include one or more (two are shown in this example) shield/heatsink layers 588, which may include materials such as, for example,Aluminum, Tungsten (a refractory metal), Copper, silicon or cobalt basedsilicides, or forms of carbon such as carbon nanotubes, and may belayered itself as described herein FIG. 3. Each shield/heat sink layer588 may have a thickness range of about 50 nm to about 1 mm, forexample, about 50 nm, about 100 nm, about 200 nm, about 300 nm, about500 nm, about 0.1 um, about 1 um, about 2 um, and about 10 um.Shield/heat sink layer 588 may include isolation openings 587, andalignment mark openings (not shown), which may be utilized for shortwavelength alignment of top layer (donor) processing to the acceptorwafer alignment marks (not shown). Shield/heat sink layer 588 mayinclude one or more shield path connects 585 and shield path vias 583.Shield path via 583 may thermally and/or electrically couple and connectshield path connect 585 to acceptor wafer 510 interconnect metallizationlayers such as, for example, exemplary acceptor metal interconnect 581(shown). Shield path connect 585 may also thermally and/or electricallycouple and connect each shield/heat sink layer 588 to the other and toacceptor wafer 510 interconnect metallization layers such as, forexample, acceptor metal interconnect 581, thereby creating a heatconduction path from the shield/heat sink layer 588 to the acceptorsubstrate 595, and a heat sink (not shown). Isolation openings 587 mayinclude dielectric materials, similar to those of BEOL isolation 596.Acceptor wafer 510 may include first (acceptor) layer metal interconnect591, acceptor wafer transistors and devices 593, and acceptor substrate595. Various topside defect anneals may be utilized. For thisillustration, an optical beam such as the laser annealing previouslydescribed is used. Optical anneal beams may be optimized to focus lightabsorption and heat generation within or at the surface of S/D layer 503and provide surface smoothing and/or defect annealing (defects may befrom the cleave and/or the ion-cut implantation) with exemplarysmoothing/annealing ray 566. The laser assisted smoothing/annealing withthe absorbed heat generated by exemplary smoothing/annealing ray 566 mayalso include a pre-heat of the bonded stack to, for example, about 100°C. to about 400° C., and/or a rapid thermal spike to temperatures aboveabout 200° C. to about 600° C. Additionally, absorber layers or regions,for example, including amorphous carbon, amorphous silicon, and phasechanging materials (see U.S. Pat. Nos. 6,635,588 and 6,479,821 toHawryluk et al. for example), may be utilized to increase the efficiencyof the optical energy capture in conversion to heat for the desiredannealing or activation processes. Moreover, multiple pulses of thelaser may be utilized to improve the anneal, activation, and yield ofthe process. Reflected ray 563 may be reflected and/or absorbed byshield/heat sink layer 588 regions thus blocking the optical absorptionof ray blocked metal interconnect 581. Annealing of dopants or annealingof damage in back channel layer 502 and/or BOX 510 and/or S/D layer 503,such as from the H cleave implant damage, may be also accomplished by aset of rays such as repair ray 565, illustrated is focused on backchannel layer 502. Heat generated by absorbed photons from, for example,smoothing/annealing ray 566, reflected ray 563, and/or repair ray 565may also be absorbed by shield/heat sink layer 588 regions anddissipated laterally and may keep the temperature of underlying metallayers, such as metal interconnect 581, and other metal layers below it,cooler and prevent damage. Shield/heat sink layer 588 and associateddielectrics may laterally spread and conduct the heat generated by thetopside defect anneal, and in conjunction with the dielectric materials(low heat conductivity) above and below shield/heat sink layer 588, keepthe interconnect metals and low-k dielectrics of the acceptor waferinterconnect layers cooler than a damage temperature, such as, forexample, about 400° C. A second layer of shield/heat sink layer 588 maybe constructed (shown) with a low heat conductive material sandwichedbetween the two heat sink layers, such as silicon oxide or carbon doped‘low-k’ silicon oxides, for improved thermal protection of the acceptorwafer interconnect layers, metal and dielectrics. Shield/heat sink layer588 may act as a heat spreader. Electrically conductive materials may beused for the two layers of shield/heat sink layer 588 and thus mayprovide, for example, a Vss and a Vdd plane and/or grid that may beconnected to the donor layer transistors above, as well may be connectedto the acceptor wafer transistors below, and/or may provide belowtransferred layer device interconnection. Noise on the power grids, suchas the Vss and Vdd plane power conducting lines/wires, may be mitigatedby attaching/connecting decoupling capacitors onto the power conductinglines of the grids. The decoupling caps, which may be within the secondlayer (donor, for example, donor wafer device structures) or first layer(acceptor, for example acceptor wafer transistors and devices 593), mayinclude, for example, trench capacitors such as described by Pei, C., etal., “A novel, low-cost deep trench decoupling capacitor forhigh-performance, low-power bulk CMOS applications,” ICSICT (9^(th)International Conference on Solid-State and Integrated-CircuitTechnology) 2008, October 2008, pp. 1146-1149, of IBM. The decouplingcapacitors may include, for example, planar capacitors, such as poly tosubstrate or poly to poly, or MiM capacitors (Metal-Insulator-Metal).Shield/heat sink layer 588 may include materials with a high thermalconductivity greater than 10 W/m-K, for example, copper (about 400W/m-K), aluminum (about 237 W/m-K), Tungsten (about 173 W/m-K), PlasmaEnhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD DLC (about1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene (about 5000W/m-K). Shield/heat sink layer 588 may be sandwiched and/orsubstantially enclosed by materials with a low thermal conductivity(less than about 10 W/m-K), for example, silicon dioxide (about 1.4W/m-K). The sandwiching of high and low thermal conductivity materialsin layers, such as shield/heat sink layer 588 and under & overlyingdielectric layers, spreads the localized heat/light energy of thetopside anneal laterally and protects the underlying layers ofinterconnect metallization & dielectrics, such as in the acceptor wafer510, from harmful temperatures or damage. When there may be more thanone shield/heat sink layer 588 in the device, the heat conducting layerclosest to the second crystalline layer or oxide layer 580 may beconstructed with a different material, for example a high melting pointmaterial, for example a refractory metal such as tungsten, than theother heat conducting layer or layers, which may be constructed with,for example, a lower melting point material, for example such asaluminum or copper. Now transistors may be formed with low effectivetemperature (less than approximately 400° C. exposure to the acceptorwafer 510 sensitive layers, such as interconnect and device layers)processing, and may be aligned to the acceptor wafer alignment marks(not shown) as described in the incorporated references. This mayinclude further optical defect annealing or dopant activation steps. Theremaining SOI donor wafer substrate 500 may now also be processed, suchas smoothing and annealing, and reused for additional layer transfers.The insulator layer, such as deposited bonding oxides (for example oxidelayer 580) and/or before bonding preparation existing oxides (forexample the BEOL isolation 596 on top of the topmost metal layer ofshield/heat sink layer 588), between the donor wafer transferredmonocrystalline layer and the acceptor wafer topmost metal layer, mayinclude thicknesses of less than about 1 um, less than about 500 nm,less than about 400 nm, less than about 300 nm, less than about 200 nm,or less than about 100 nm.

As illustrated in FIG. 5D, transistor and back channel isolation regions505 and/or transistor isolation regions 586 may be formed. Transistorisolation region 586 may be formed by mask defining and plasma/RIEetching SID layer 503, substantially to the top of BOX layer 501 (notshown), substantially into BOX layer 501, or back channel layer 502 (notshown). Transistor and back channel isolation regions 505 may be formedby mask defining and plasma/RIE etching channel layer 503, BOX layer 501and back channel layer 502, substantially to the top of oxide layer 580(not shown), substantially into oxide layer 580, or further into the topBEOL dielectric layer in acceptor wafer 510 (not shown). Thusintermediate S/D region 523 may be formed, which may substantially formthe transistor body, back-channel region 522 may be formed, which mayprovide a back bias and/or Vt of the eventual transistor channel.Back-channel region 522 may be ion implanted for Vt control and/or bodybias efficiency. A low-temperature gap fill dielectric, such as SACVDoxide, may be deposited and chemically mechanically polished, the oxideremaining in transistor and back channel isolation regions 505 andtransistor isolation regions 586. An optical step, such as illustratedby exemplary STI ray 567, may be performed to anneal etch damage anddensify the STI oxide in transistor and back channel isolation regions505. The doping concentration of intermediate S/D region 523 may includevertical or horizontal gradients of concentration or layers of differingdoping concentrations. The doping concentration of back-channel region522 may include vertical or horizontal gradients of concentration orlayers of differing doping concentrations. The optical anneal, such asexemplary STI ray 567, and/or exemplary implant ray 569 may be performedat separate times and processing parameters (such as laser energy,frequency, etc.) or may be done in combination or as one optical anneal.Optical absorber and or reflective layers or regions may be employed toenhance the anneal and/or protect the underlying sensitive structures.Moreover, multiple pulses of the laser may be utilized to improve theanneal, activation, and yield of the process. BOX region 531 may be arelatively thin dielectric, including the thickness range of about 5 nmto about 100 nm, at least a portion of which being between theback-channel region 522 and intermediate S/D region 523. Back-channelregion 522 could be constructed from a material that would not bedamaged by the optical anneal process. Such could be a refractory metalor doped silicon in crystallized form, poly or amorphous, or otherconductive material that are acceptable for semiconductor processing andcan withstand high temperature of about 700° C. or higher.

As illustrated in FIG. 5E, an undoped transistor channel may be formedwithin the intermediate S/D region 523. Regions of intermediate S/Dregion 523 may be lithographically defined and etched away, clearing theeventual channel region of substantially any silicon material and mayetch slightly into BOX region 531. Undoped amorphous silicon or polysilicon may be deposited to fill the eventual channel region. A CMPprocess may be utilized to remove substantially all of the depositedamorphous silicon or polysilicon not in the etched regions, thus formingundoped channel region 534 and S/D & LDD regions 535. The CMP processmay be performed to overpolish and remove a small portion of the tops ofS/D & LDD regions 535, back channel isolation regions 505, andtransistor isolation regions 586, and any smeared doping material fromthe S/D & LDD regions 535 may be removed by <400 C oxidation and striputilizing a process such as the TEL SPA tool described herein and inincorporated patent references. The amorphous silicon or polysilicon inundoped channel region 534 may be crystallized to a nearmono-crystalline state by optical annealing such as illustrated byexemplary channel smoothing ray 568, by nano epitaxial ordering from thesidewalls of the mono-crystalline S/D & LDD regions 535. Remainingdamages and surface roughness may also be repaired and smoothedrespectively by optical annealing, such as illustrated by exemplarychannel smoothing ray 568.

As illustrated in FIG. 5F, a transistor forming process, such as aconventional HKMG with raised source and drains (SID), may be performed.For example, a dummy gate stack (not shown), utilizing oxide andpolysilicon, may be formed, gate spacers 530 may be formed, raised S/Dregions 532 and channel stressors may be formed by etch and epitaxialdeposition, for example, of SiGe and/or SiC depending on P or N channel(and may be doped in-situ or ion-implantation and optical annealactivation), LDD, halo, and S/D ion-implantations may be performed, andfirst ILD 536 may be deposited and CMP′d to expose the tops of the dummygates. Thus transistor channel region 534 and S/D & LDD regions 535 maybe formed. The dummy gate stack may be removed and a gate dielectric 507may be formed and a gate metal material gate electrode 508, including alayer of proper work function metal (Ti_(x)Al_(y),N_(z) for example) anda conductive fill, such as aluminum, and may be deposited and CMP′d. Thegate dielectric 507 may be an atomic layer deposited (ALD) gatedielectric that may be paired with a work function specific gate metalin the industry standard high k metal gate process schemes, for example,as described in the incorporated references. Alternatively, the gatedielectric 507 may be formed with a low temperature processes including,for example, LPCVD SiO₂ oxide deposition (see Ahn, J., et al.,“High-quality MOSFET's with ultrathin LPCVD gate SiO2,” IEEE ElectronDevice Lett., vol. 13, no. 4, pp. 186-188, April 1992) or lowtemperature microwave plasma oxidation of the silicon surfaces (see Kim,J. Y., et al., “The excellent scalability of the RCAT(recess-channel-array-transistor) technology for sub-70 nm DRAM featuresize and beyond,” 2005 IEEE VLSI-TSA International Symposium, pp. 33-5,25-27 Apr. 2005) and a gate material with proper work function and lessthan approximately 400° C. deposition temperature such as, for example,tungsten or aluminum may be deposited. Furthermore, the gate dielectricon transistors may have different dielectric permittivities than silicondioxde. The gate dielectric permittivity of the second layer transistorsmay be different than the gate dielectric permittivity of the firstlayer transistors. An optical step, such as represented by exemplaryanneal ray 521, may be performed to densify and/or remove defects fromgate dielectric 507, anneal defects and activate dopants such as LDD andS/D implants, densify the first ILD 536, form DSS junctions (DopantSegregated Schottky such as NiSi₂), and/or form contact and S/Dsilicides (not shown). The optical anneal may be performed at eachsub-step as desired, or may be done at prior to the HKMG deposition(such as after the dummy gate but before the HKMG formation), or variouscombinations. Optionally, portions of transistor isolation region 586and BOX region 531 may be lithographically defined and etched away, thusforming second transistor isolation regions 576 and PD transistor area518. Partially depleted transistors (not shown) may be constructed in asimilar manner as the FD-MOSFETs constructed on transistor channelregion 534 herein, but now with the thicker back-channel region 522silicon as its channel body. PD transistor area 518 may also be utilizedto later form a direct connection thru a contact to the back-channelregion 522 for back bias and Vt control of the transistor withtransistor channel region 534. If no PD devices are desired, then it maybe more efficient to later form a direct connection thru a contact tothe back-channel region 522 for back bias and Vt control of thetransistor with transistor channel region 534 by etching a contact thrutransistor isolation region 586. Raised S/D regions 532 may be formed bylow temperature (less than about 400° C.) deposition of in-situ dopedpolysilicon or amorphous silicon into the S/D openings, an opticalanneal to further crystallize and dopant activate the raised S/Dmaterial, and removal of excess raised S/D material. Further processingto connect the transistors and make vertical connections may follow theprocessing described in at least FIGS. 46F and 46G of incorporatedreference U.S. Pat. No. 8,574,929.

The various layers of a 3D device may include many types of circuitry,which may be formed by regions of transistors and other semiconductordevice elements within that layer or in combination with other layers ofthe 3D device, and connections between the transistors within the sameregion, region to region and vertically (layer to layer. stratum tostratum) may be provided by layers of interconnect metallization andvertical connections such as TLVs and TSVs. In addition, power routingwithin the 3D device may utilize thicker and/or wider (more conductive)interconnect metallization than another layer, especially if the layeris closest to the source of external power and/or has a greater currentload/supply requirement. Many individual device and interconnectembodiments for 3D devices have been described herein and in theincorporated patent references. As illustrated in FIG. 6 herein, someadditional embodiments and combinations of devices, circuits, paths, andconnections are described and may utilize similar materials,constructions and methods as the incorporated references or discussedherein. With reference to embodiments described, for example, hereinand, with respect to FIG. 46 of incorporated reference U.S. Pat. No.8,574,929, and in the disclosures of many of the other incorporatedpatent references, a substrate layer, which may have a thicker body thanother semiconductor layers above or within the 3D device, such asacceptor 610, may be formed and may include heat sink 697, acceptorsubstrate 695, acceptor wafer transistors and circuits 693, first(acceptor) layer metal interconnect 681 which may include first layercontacts 691, first layer vias 683, at least one shield layer/region 688(two layers and many regions, such as lower level shield layer region685, shown), interconnect insulator regions 696 and ESD diode structures607. A second semiconductor layer may be transferred and constructed ontop of the first layer with isolation layer 680 in-between and verticallayer to layer interconnections may be provided by TLV/TSV 635, only oneis shown. A layer of transistors and circuits 622 may include secondlayer input device structures 676, FD ESD structures 617, Phase LockLoop circuits PLL 618, SERDES circuitry 619, and output device structure651. Second interconnections layer 630 may include at least onelayer/regions of metallization and associated contacts and via, forexample, second layer metallization M1 segments 628, 621, 623, 625,second layer contacts 626, second layer vias 652, and conductive pads690. The 3D device may be connected to external devices utilizing manystructures known to those of ordinary skill in the art, for example,bond wires 699. Input device structures 676 and output device structure651 may be connected to external devices through, for example, secondlayer contacts 626, second layer metallization M1 segments 628, secondlayer vias 652, conductive pads 690, and bond wires 699. A portion ofthe transistors within input device structures 676 and output devicestructure 651 may be larger in either or both width and length than mosttransistors within acceptor wafer transistors and circuits 693, and mayhave a different gate oxide, in thickness and/or composition. Inputdevice structures 676 (and output device structure 651) may be subjectedto voltage and/or current transients from external devices or generatedexternally and traveling to the 3D device along bond wires 699. Inputdevice structures 676 (and output device structure 651) may be protectedby dissipating the transient energy in diode structures, such as ESDdiode structures 607 on the relatively thicker (than for example, thesecond semiconductor layer) acceptor substrate 695, which may beconnected by a multiplicity of connection stacks such as first(acceptor) layer metal interconnect 681 which may include first layercontacts 691, first layer vias 683, at least one shield layer/region688, TLV/TSV 635, and second layer metallization M1 segments 628. Inputdevice structures 676 (and output device structure 651) may be protectedby dissipating the transient energy in a transient filtering circuitrysuch as for example, FD ESD structures 617, which may reside on arelatively thin semiconductor layer in the 3D device and may effectivelyutilize fully depleted transistors in the filter circuitry. FD ESDstructures 617 may be coupled to input device structures 676 (and outputdevice structure 651) by second layer interconnections (not shown).Input device structures 676 may be connected to PLL 618, for example,thru second layer metallization M1 segment 621 and second layer contacts626. Input device structures 676 may be connected to SERDES circuitry619, for example, thru second layer metallization (not shown). Amonolithic 3D stack, wherein at least one of the layers in the stack isvery thin (less than about 200 nm), may provide an unexpected benefit.The thicker substrate may be used for energy dissipating diodes tohandle large energy transients and the thin (‘second’ or ‘third’ etc.)layer may be used for a high frequency switching capability to protectagainst a high frequency transient on the input lines. This may be donesimultaneously on an I/O. Furthermore, one style could be chosen forspecific I/Os as well. The monolithic 3D structure (thin/thick) alsoprovides a low capacitance drive output and very fast input devicestructure (‘fully depleted’ transistors), yet still be protected fromhigh energy transients that could be dissipated in the bulk (firstlayer). This ‘two-tier’ ESD structure invention could also provide costeffective I/Os anywhere throughout the area of the device, as the largersized (area-wise) diodes could be placed underneath the second layerinput transistors. This would also provide a closer than 2D layoutcoupling of the I/O to the other chip circuitry, as the large energydissipating diodes are not on the same level as the circuitry proper,and would not interfere with the data circuitry operation (noise).Output device structures 651 may be connected to SERDES circuitry 619,for example, thru second layer metallization M1 segment 623 and secondlayer contacts 626. Output device structures 651 may drive signals thruthe connection to conductive pads 690 and then out to external devicesthru bond wires 699. Transistors within a lower layer, for examplewithin acceptor wafer transistors and circuits 693, may be connected(not shown) to the output device structure 651 and drive a signal to theoutput device structure 651, and a portion of the transistors of outputdevice structure 651 may have a larger width and/or length than thetransistors within acceptor wafer transistors and circuits 693. Powerfrom external sources may be routed thru bond wires 699 to conductivepads 690 to the 3D device, wherein at least a portion of the secondinterconnections layer 630 may be constructed with thicker and/or widermetallization wiring (for example 4× wiring as described in incorporatedpatent references) so to provide the higher current carrying capabilityrequired for the second layer power distribution grid/network than thatof the lower layer, in this example, first layer metallization wiring(for example 1× or 2× wiring as described in incorporated patentreferences). The width and/or length of the transistors of the secondlayer of transistors and circuits 622, for example a portion of those insecond layer input device structures 676 and/or FD ESD structures 617and/or output device structures 651, may be substantially larger thanthe width and/or length of transistors in acceptor wafer transistors andcircuits 693. Local ESD clamps or triggering elements may be constructedwith the bulk or FD devices, and the FD (UTBB) devices may beband-modulation devices such as the FED (Field Effect Diode), Z²-FET(Zero impact ionization and Zero sub-threshold swing) or BBCT(SOI-BackBiasControlled-Thyristor). One example in 2D may be found in Y.Solaro, et al., “Innovative ESD protections for UTBB FD-SOI Technology,”IEEE IEDM 2013, paper 7.3, the contents fully incorporated herein byreference. The back-gate/bias plane may be accomplished with anintegrated device, for example, a back-channel region 522 or by a baselayer (or layer below) top metal plate/line (for example, such as thetopmost shield layer/region 688) in a monolithic 3D configuration. In amonolithic 3D configuration as disclosed herein and in the incorporatedreferences, the layers above the base/substrate layer are naturallyconstructed SOI, wherein the above techniques to create the back gatecontrolled ESD structures may be accomplished without the complexity of2D processing of the buried layers and connections. Design of the ESDprotection for, for example, a single-pole multiple throw (SPMT) Tx/Rxswitch for multi-mode smart phones, may include a series shunt topologywhere each path has a series branch to the antenna and a shunt branch toground (one example in 2D may be found in X. S. Wang, et al. IEEE S3SConference 2013 paper “Concurrent Design Analysis of A 8500V ESDprotected SP10T Switch in SOI CMOS,” the contents fully incorporatedherein by reference. Feed-forward capacitors (FFCs) may be used to keepan even distribution of AC voltage drops across the shunt branches. TheFFCs may be constructed in the same layer as the shunts (preferably anRF optimized layer), the layer below or the layer above. This allowsflexibility in type, value, and/or the ability to adjust (hard wired,electrically programmable, or top-layer laser/e-fuse programmable) eachof the shunts effective FFC value.

Conductive pads 690 and associated I/O circuits and any redistributionlayers may be arranged and lay-ed out in many configurations. Forexample, conductive pads 690 may be designed and lay-ed out as aperimeter bond pad grouping or as an array I/O wherein the conductivebond pads may be arrayed throughout the area of the die when viewed fromabove or below. Conductive pads 690, whether arrayed in area orperimeter, may include the associated I/O and/or ESD circuitrypositioned vertically below (or above for ‘backside pads’) theconductive pads and on the same layer/stratum, vertically below (orabove for ‘backside pads’) on a layer/stratum not the same as theconductive pad layer/stratum, or not vertically below (or above for‘backside pads’) the conductive pad, yet on the same layer/stratum asthe conductive pads 690 or on a layer/stratum not the samelayer/stratum. Array packages may include the PGA, BGA, FBGA, Fan-inQFN, and Fan-out WLPs and may utilize attachments such as solder ballsor columns.

Stress relief from wire bonding, ball bonding, column attaching may bemitigated in the 3DIC stack. For example, conductive bond pad 690 may bereplicated in full or in part down one or more layers/stratum directlybelow, and this ‘stack of bond pads’ may extend to the substrate 695.Bonding stresses may be mitigated by forming a relatively soft layer orregion underneath conductive bond pads 690, for example a low-kdielectric and/or an aero-gel. In addition, a region or layer of aconductive aerogel may be formed underneath conductive pad 690 thatwould allow at least a one-time crush and still maintain conductivityand reliability. A combination of a hard layer and then a soft layer mayalso be employed below conductive pads 690. Young's modulus may be ameasure of soft and hard. A MEMS structure, for example a torsion springassembly, may be formed directly underneath the bonding area ofconductive pad 690.

Persons of ordinary skill in the art will appreciate that theillustrations in FIG. 6 are exemplary and are not drawn to scale. Suchskilled persons will further appreciate that many variations may bepossible such as, for example, a thick enough semiconductor layer toenable ESD diode style protection circuitry to be constructed need notonly be on the base or substrate layer, but may reside elsewhere in the3D device stack. Moreover, the output circuitry including output devicestructures 651 may wholly or partially reside on a semiconductortransistor layer that is not on top, and vertical connections includingTLVs/TSV may be utilized to connect the output device structures 651 toconductive pads 690. Furthermore, the input circuitry including inputdevice structures 676 may wholly or partially reside on a semiconductortransistor layer that is not on top, and vertical connections includingTLVs/TSV may be utilized to connect the input device structures 676 toconductive pads 690. Similarly, SERDES circuitry and 619 PLL 618 maywholly or partially reside on a semiconductor transistor layer that isnot on top, these choices being one of design choice and devicecharacteristics driven. Furthermore, connection to external devices(signal and/or power supply) may be made on the backside of acceptorsubstrate 695. Moreover, connection to external devices form the 3Ddevice may utilize many types of structures other than bond wires 699shown in the illustration, for example, flipchip and bumps, and/orwireless circuitry. Thus the invention is to be limited only by theappended claims.

A 3D system, such as has been described herein and in relation to atleast FIG. 11 and FIG. 12 of incorporated reference U.S. Pat. No.8,378,715, is not limited to a configurable system and could be used inother types of platform configurations. The strata of such a 3D systemcould be connected by TSV and might use an interposer or be directlyplaced one on top of the other. Also the strata might be connected bywhat has been called in this application and the patents, publications,and applications that are incorporated by reference, through layer via(“TLV”) where the layer carrying the transistor may be thin (below about2 micron or below about 100 nm in thickness or below about 30 nm inthickness).

FIG. 7 illustrates a 3D platform constructed accordingly. Platform base701 could be the same type of stratum, for example, a Phone Processor,which may be overlaid by and connected to a second stratum 712, forexample, a memory stratum. This platform could be produced in highvolume and could be stocked in wafer form or die form. A market specific3D system could be constructed by overlaying and connecting to theplatform (formed by platform base 701 and second stratum 712), a thirdstratum which maybe designed and manufactured for a specific market, forexample, a Radio for US 702, a Radio for Europe 704 or a Radio for China706. The system could be constructed of stratum on top of a stratuminterconnected by TSV or TLV or side by side wiring using, what is nowcalled by the industry, interposers. There are many advantages for sucha 3D platform, including reduced cost of the common element design,reduced cost of volume manufacturing, and shorter time to market and tovolume for any new specific market that need only few, and ideally onlyone, customized stratum and the remainder of the system a similar set ofstratums.

Additional embodiment for a 3D platform is to use a variation of stratawhich might include in some platforms a single stratum of memory and inanother platform two strata of memory offering a larger memory. Anothervariation could use a different amount of programmable logic rangingfrom no programmable logic to multiple strata of programmable logic.Another variation could add special system input/output resourcesranging from no SERDES to one or more strata of I/O (Input Output) thatmay include various amounts of SERDES enabled I/O.

Additional advantage for having the memory layer first and the logic ontop of it is for using the bulk silicon for the memory layer. FIG. 8illustrates a cross-section picture of a device that includes trenchcapacitor 802. The trench capacitor is a known technique forconstructing DRAM (Dynamic Random Access Memory) or embedded DRAMmemory. The trench might be few tenths of a micron deep to a couple ofmicrons, and forming the trench on the bottom most layer can be veryeffective. Another type of memory that could benefit from being formedon the bulk silicon or substrate are two-state stable floating bodymemory as described in U.S. Pat. No. 8,206,302 which is incorporatedherein by reference. In the two-stable states floating body memory, adeep implant of n+ layer in the bulk may be used to provide a back biasto the floating body, so to form a two-state stable memory. A similarstructure could be formed on layers other than the bottom-most layer,yet it might be preferred to use the bulk of the bottom layer for such amemory layer.

Another alternative is to use the trench capacitor 802 to help stabilizethe power lines. It is well known technique in the art to use capacitorsto stabilize power lines in electronic circuits. In a 3D system a trenchcapacitors in the bulk could help stabilize power lines and not just forthe bottom-most layer but also for the upper layers of circuits.

In many 3D systems it is useful to construct the power delivery buses toall circuit layers in a substantially uniform or a substantiallyperiodic structure. FIG. 9 is a drawing illustration of a 3D devicepower distribution or power delivery structure. The bottom-mosttransistor layer 916 may include the bulk silicon which sometimes mightbe called the base layer. The upper most transistor layer 914 may be thesecond layer, as shown (there may be more than two layers or stratum).The main system power distribution sub-structures 910 may be connectedto the external source of power and provide the first horizontal powerdistributions. The per-layer power distribution is illustrated by secondlayer power distribution 908 and first layer power distribution 906. InFIG. 9 the power distribution may include the two main power sourcesoften called Vss and Vdd, or power and ground. In many 3D systems thepower distribution may include additional power lines for voltages otherthan Vss and Vdd as sometime might be required. In some 3D systems atleast one layer/stratum may use a different voltage than the otherlayers or stratum, as often will be the case when Flash types of memoryor some analog circuitry is used. It might be preferred to place thespecial voltages on dedicated layers and form most layers with just onepower and one ground. It might be preferred to keep the multiplevoltages layer as the upper-most layer, and drive power to lower layershaving a lower number of different power types/voltages. The 3Dintegrated circuit could have a similarly designed and laid-outdistribution networks, such as for ground and other supply voltages, aswell. The power grid may be designed and constructed such that eachlayer or strata of transistors and devices may be supplied with adifferent value Vdd. For example, bottom-most transistor layer 916 maybe supplied by its power grid to have a Vdd value of 1.0 volts and uppermost transistor layer 914 a Vdd value of 0.8 volts (or, for example,about 10 v to program a NV memory). Furthermore, the global power grid0910 wires may be constructed with substantially higher currentconduction, for example 30% higher, 50% higher, 2× higher, than localpower grids, for example, such as first local power grid 0906 wires andsecond local power grid 0908 wires. The thickness, linewidth, andmaterial composition for the global power grid 0910 wires may providefor the higher current conduction, for example, the thickness of theglobal power grid 0910 wires may be twice that of the local power gridwires and/or the linewidth of the global power grid 0910 wires may be 2×that of the local power grid wires. Moreover, the global power grid 0910may be optimally located in the top strata or layer of transistors anddevices. Noise on the power grids, such as the Vss and/or Vdd supplygrids, may be mitigated by attaching/connecting decoupling capacitorsonto the power conducting lines of the grid(s), such as global powergrid 0910, first local power grid 0906 wires and second local power grid0908 wires. The decoupling caps may include, for example, trenchcapacitors such as described by Pei, C., et al., “A novel, low-cost deeptrench decoupling capacitor for high-performance, low-power bulk CMOSapplications,” ICSICT (9^(th) International Conference on Solid-Stateand Integrated-Circuit Technology) 2008, October 2008, pp. 1146-1149, ofIBM. The decoupling capacitors may include, for example, planarcapacitors, such as poly to substrate or poly to poly, or MiM capacitors(Metal-Insulator-Metal). FIG. 9 illustrates the connection of the powerbetween layers (such as upper most transistor layer 914 and bottom-mosttransistor layer 916) utilizing first vertical connection 902 and secondvertical connection 904. It may be advantageous to design the powerconnection, such as for example TLVs or TSV, or a multiplicity of TLVsor TSVs, between layers aligned one on top of the other as illustratedin FIG. 9 by first vertical connection 902 and second verticalconnection 904. Such aligned power connection could be connected totrench capacitors, such as for example trench capacitors 802, which mayreside in the bulk silicon of bottom-most transistor layer 916. Secondlayer vias 0918 and first layer vias 0912, such as the TSV or TLV, couldbe used to transfer the supply voltage from the global power grid 0910to second local power grid 0908 and first local power grid 0906.Additionally such aligned power distribution structures between layerscould efficiently channel the heat generated at the various layers downto the bulk silicon and from there to the device heat-sink 936 and/or toan external surface of the device (not shown).

While the previous discussion described how an existing powerdistribution network or structure could be designed/formed and they cantransfer heat efficiently from logic/memory cells or gates in 3D-ICs totheir heat sink, many techniques to enhance this heat transfercapability will be described herein and in at least incorporatereference U.S. Pat. No. 8,803,206. Many embodiments of the invention canprovide several benefits, including lower thermal resistance and theability to cool higher power 3D-ICs. As well, thermal contacts mayprovide mechanical stability and structural strength to low-k Back EndOf Line (BEOL) structures, which may need to accommodate shear forces,such as from CMP and/or cleaving processes. The heat transfer capabilityenhancement techniques may be useful and applied to differentmethodologies and implementations of 3D-ICs, including monolithic 3D-ICsand TSV-based 3D-ICs. The heat removal apparatus employed, which mayinclude heat sinks and heat spreaders, may include an external surfacefrom which heat transfer may take place by methods such as air cooling,liquid cooling, or attachment to another heat sink or heat spreaderstructure

In 3D systems, a portion of the layers/strata might be dedicated tomemory and a portion to logic. The memory layer could include varioustype of memory such SRAM, DRAM, Floating Body RAM, R-RAM and Flashtypes. The memory layer might include the memory control circuits andmemory peripheral circuits or those could be in a layer above or belowthe memory layer. The memory could be constructed on a single layer ormight include two or more layers. An effective option could be to usetwo or more layers of memories utilizing an architecture such as havebeen presented in the incorporated by reference patents, publications,and applications, wherein a lithography step may be used to pattern twoor more layers together, thus reducing the overall cost by sharing thecostly step of lithography across two or more layers. Some memory layerscould be dedicated to a single type of memory or to mix of various typesof memory. For example, a compute layer may be supported by multiplelayers of memory processed with lithography that is shared across thesemultiple layers, and where these layers may include non-volatile memoryto hold the program and volatile memory to hold data.

An attractive advantage of having the memory decoders and logic abovethe memory layer wherein the memory layer may be an array of bit cells,relates to an option of pre-patterning the transferred layer prior tothe layer transfer. In such a case many high temperature steps could beperformed on that layer before the layer transfer, such as formingtrench isolation or even full transistors as has been presented in atleast U.S. Pat. No. 8,273,610 and before in relation to FIG. 19 ofincorporated reference U.S. Pat. No. 8,378,715. Accordingly atransferred layer misalignment could be reduced when the transfer layeris patterned with a repeating pattern. The same concept could beinverted, with a non-repeating layer transferred on top of a repeatingone. Accordingly, the alignment error could be reduced to about the sizeof the repeating element, the bit cell. This approach is similar to themethod presented in relation to FIG. 19 of incorporated reference U.S.Pat. No. 8,378,715, except that in this case the shift to compensate forthe misalignment may be done in respect to the bit-cell array. Thisapproach will require a relatively larger window to be etched so therequired memory could be sized through the overlaying transferred layerand then a connection to the bit lines and word lines could be made byincluding large enough landing zones/strips to connect to them.

In such way a single expensive mask set can be used to build many wafersfor different memory sizes and finished through another mask set that isused to build many logic wafers that can be customized by few metallayers.

Many devices may have at least one processor on chip and often more thanone. In most cases these processors use at least one bus to commonlycommunicate with multiple sub systems such as memory and peripherals.FIG. 10 is a drawing illustration of an exemplary system that uses aprocessor such as, for example, ARM processor 1001 that is connecteddirectly with cache memory 1003 and using a bus 1002 to connect to atleast two sub-systems, such as, for example, Hardware Acceleration 1004and graphic controller 1006. Bus 1002 could be used by a secondprocessing unit such as DSP 1008 to connect to other elements in theoverall system. Such a system could also include additional secondarybus 1012 to manage the connection of peripheral units such as, forexample, USB Controller 1014 and Digitizer 1016. In many cases a designobjective may be to achieve a higher speed of processor operation or toreduce power by making the lines constructing the bus shorter. In a 3Dsystem such objective might be achieved, for example, by properlysplitting/partitioning the subsystems connecting to the bus 1002 betweenthe stratum the processor 1001 is on and another stratum that is eitherabove it or below it. (See, for example, FIG. 11A, an exemplary 3Dsystem/device 1100 with exemplary elements, such as, a processor suchas, for example, ARM processor 1001, cache memory 1003, a portion of bus1002 located on the first stratum, Hardware Acceleration 1004, DSP 1008,on-chip memory, graphic controller 1006, and a portion of bus 1002located on the second stratum which may be connected to the portion ofbus 1002 located on the first stratum utilizing TLVs 1190). Anotherobjective related to such splitting/partitioning relates to the factthat some of the units, for example, graphic controller 1006, USBController 1014 and Digitizer 1016, have at least one (typically many)connection to external devices, and it may be desired to place thoseparticular logic units on the strata closer to the connection to theexternal devices, which in some cases might be the top-most stratum.Many types of buses may be utilized in a 3D system, such as, forexample, an Advanced Microcontroller Bus Architecture (AMBA) bus, aCoreConnect bus, a STBus, a Wishbone bus, an Open Core Protocol (OCP)bus, or a Virtual Component Interface (VCI) bus.

As illustrated in FIG. 11B, one such splitting/partitioning approachcould suggest first placing the logic units that are connected to thebus and have an external connection on the upper stratum. Then, if thetotal area of these units is less than half of the total area of all theunits connected to that bus, start assigning units to the lower stratumfrom the bigger units to the smaller until the area of those assigned tothe lower stratum just exceeds the area of those logic units assigned tothe upper stratum. Then assign the biggest un-assigned unit to the uppertier and repeat. If the total area of these units (those units firstassigned to the upper stratum) is greater than half of the total area ofall the units connected to that bus, then move the unit with the leastnumber of external connections may be moved to the lower stratum(outside if possible for potentially better connectivity), and repeat ifnecessary to bring the upper stratum assigned area to just below 50% ofthe total area of all the units connected to that specific bus.

FIG. 12A is a drawing illustration of different Clock distributionnetwork styles. Many logic circuits or logic units may use a clock treeto distribute a clock signal to the Flip-Flops. A common style of clocktree is the H-Clock Tree 1202. The origin point of the clock signal 1212is driving a first H-Tree from the center of the H. Subsequently, eachend-point of the H is an origin of the next H 1216, and so forth. Thefinal edge 1224 drives the individual Flip-Flop cluster 1218.

In some cases it may be desired to reduce the skew between edges asillustrated in the branch tree 1204 wherein clock tree branches 1214 areshorted by cross-link 1222. Another style of clock distribution iscalled Mesh 1206 where a grid of connection is used to distribute theclock signal. These schemes may be combined to form a hybrid 1208 wherea tree 1220 may be added to a grid 1225. In a 3D device it might bedesired to split logic circuits between at least two strata includingcircuits that share the same clock domain In such case it might bedesired to first connect the clock origin to each strata that hascircuits that use that clock domain, then to construct within eachstratum a clock distribution structure that might include a clock treesuch as, for example, H tree, or grid and tree combination or otherclock distribution scheme used in the art. (See, for example, FIGS. 12Band 12C, for exemplary 3D system/device clock distribution networksH-Clock 1292, Mesh 1296, branch tree 1294, hybrid 1298). Some circuitscould have an interaction between strata wherein a signal may begenerated in one stratum and that signal is used and latched on anotherstratum, and accordingly the skew between Flip-Flop on one stratum andthe other would be reduced. A cross-link 1222 could be used betweenstratum, such as, for example, a TLV or TSV. Alternatively a grid 1224could be constructed spanning multiple stratum reducing the clock skewbetween them. In some cases the origin of the clock may be either drivenby a signal coming from outside of the 3D device or generated by acircuit on the 3D device such as for example, a Phase-Lock-Loop, whichmay be synchronized to a signal from outside of the 3D device (a clocksource may rather be provide on-chip in the 3DIC stack as suggestedlater herein). Accordingly it might be desired to first process theclock signal at the upper-most stratum and then drive it down to theorigins of the clock distribution structures at the desired stratum orstratums. The clock origin of the clock distribution structure andcircuits on one stratum may be connected to the origin of the clockdistribution structure and circuits of a second stratum, with onefeeding the other.

Distribution of a clock signal from one stratum to the next may beaccomplished with electrically conductive vertical connections, forexample, TLVs, or may be accomplished by an RF/capacitive or opticaldevice and connection between stratums. For example, a clock signalgenerated in a device layer above the substrate layer may beelectrically coupled to various points on the substrate layer below(supplying a second layer generated clock signal to a portion orsubstantially all of the substrate based transistors) utilizing a TLVconnection or connections, or an RF/capacitive or optical connection orconnections. Utilizing an only RF/capacitive or optical connection orconnections between stratums may be advantageous when it is desirable toisolate a noisy device type to a single layer, yet bring out theintended signals and not the noise. For example, and analog or RF devicelayer in a 3DIC stack could be emf shielded top and bottom (and sides ifnecessary), with only openings for a vertical RF/capacitive or opticalconnection where desired, thus minimizing the disturb effects of theanalog or RF device layer on any of the other device layers in the 3DICstack.

Scaling advanced CMOS field effect transistors face at least twoproblems that result in high power consumption: the increasingdifficulty of reducing the supply voltage and stopping the rise ofleakage currents. One device that may replace the CMOS FET is the tunnelFET (TFET). The primary injection mechanism in a TFET is interbandtunneling whereby charge carriers transfer from one energy band intoanother at a heavily doped p+-n+ junction. (In contrast, for MOSFETs thecharge carriers are thermally injected over a barrier). Ioff, the offcurrent of the TFET, is quite low due to this injection barrier and aninherently very steep subthreshold slope. However, obtaining good Ion isdifficult. High barrier transparency is vital and strong modulation bythe gate of the channel bands is critical. Thus, high permittivity gatedielectrics with as low an equivalent oxide thickness as possible aredesirable, as well as providing as thin of a channel body as possiblefor best case electron transport, plus an abrupt doping profile at thetunnel junction to maximize injection efficiency. Maximizing the gatemodulation of the tunneling barrier width can be accomplished byoverlapping the gate with the tunneling region, or designing a sourceregion covered with an intrinsic channel layer under the top gate. TFETscan be formed with a horizontally oriented channel or a verticallyoriented channel. Many types of TFETs have been developed for 2Dapplications, for example, double gate heterojunction TFET, nanowireTFET, Resonant TFET, synthetic electric field TFET, III-V based TFETs,and carbon based TFETs. Many of these can be advantageously formed in amonolithic 3D process flow. Furthermore, the gate dielectric ontransistors may have different dielectric permittivities than silicondioxde. The gate dielectric permittivity of the second layer transistorsmay be different than the gate dielectric permittivity of the firstlayer transistors.

For example, the 2D strained Si nanowire (SiNW) TFETs of L. Knoll, etal., “Demonstration of Improved Transient Response of Inverters withSteep Slope Strained Si NW TFETs by Reduction of TAT with Pulsed I-V andNW Scaling,” IEEE IEDM 2013, paper 4.4, the contents incorporated hereinby reference, may be constructed utilizing the monolithic 3D techniquesand methods disclosed in the incorporated references. For example,nanowires may be formed by patterning and etching either an amorphous-Sior a layer transferred monocrystalline silicon (may be strained Si aswell) thin layer on top of metallization layers that are on top of asubstrate of devices and circuits. HKMG gate stacks may be formed andthen very thin Ni and Al layers may be deposited to form self-alignedsource/drain silicides into which angled implants are shadow implantedto form p+ and n+ pockets on opposite sides of the gates and steepsloped abrupt junctions can be formed with dopant segregationtechniques. RTP and/or pulsed laser techniques with or without shieldingmay be employed for the thermal steps. GAA (Gate All Around) or frigatestructures may be formed as disclosed in the incorporated references.Back gates may be formed in-situ above the bonding oxides or may be fromtopmost metal layers of the layer below's shields and/or interconnectlayers, as disclosed in the incorporated references and herein (theback-gate/bias plane may be accomplished with an integrated device, forexample, a back-channel region 522 or by a base layer (or layer below)top metal plate/line (for example, such as the topmost shieldlayer/region 688) in a monolithic 3D configuration).

For example, the synthetic electric field tunnel FETs (SE-TFET) of Y.Morita, et al., “Synthetic electric filed tunnel FETs: drain currentmultiplication demonstrated by wrapped gate electrode around thinepitaxial channel,” IEEE VLSI Symposium 2013, paper 16.1, T236, thecontents incorporated herein by reference, may be constructed utilizingthe monolithic 3D techniques and methods disclosed in the incorporatedreferences. For example, highly doped source and drains may be formed ona substantially undoped monocrystalline donor substrate withion-implantation and activated as strips and then layer transferred as amonocrystalline silicon thin layer on top of metallization layers thatare on top of a substrate of devices and circuits. The source and drainsmay also be formed directly on a layer transferred substantially undopedmonocrystalline thin layer with masking and ion-implantation/PLADtechniques, and then activated with the optical and/or thermal annealingwith or without shields as disclosed in the incorporated references. Athin (about 5 nm to about 20 nm) undoped channel layer may be formedwith low temperature, for example, such as MOCVD or SP-ALD techniques,to preserve the abrupt vertical junction profile. A HKMG gate stack maybe formed, for example, an about 5 nm HfO₂ insulator and an about 40 nmTiN gate electrode deposition, and subsequent patterning and etching.Interconnect formation may then ensue. Narrow channel widths andthicknesses increase electric field effects and thus may substantiallyimprove the Ion. Backgates, for example, as described herein and in theincorporate references, may also be utilized to increase Ion anddecrease Ioff. Layer transfer of the source, channel and drain provide amonolithic 3D formation advantage to TFETs: for example, not just theaddition of a natural integrated backgate, but also the ability to use ahigher carrier mobility transferred layer such as, for example,S_(1-x)Ge_(x) or Ge, and InGaAs.

For example, the complementary hetero junction vertical TFETs (VTFET) ofR. Rooyackers, et al., “A New Complementary Hetero-Junction VerticalTunnel-FET Integration Scheme,” IEEE IEDM 2013, paper 4.21, pp. 92-94,the contents incorporated herein by reference, may be constructedutilizing the monolithic 3D techniques and methods disclosed in theincorporated references. For example, and N+Si/intrinsic Si stack may beformed on a donor wafer, flipped, bonded and layer transferred to apre-processed acceptor substrate (of completed transistors, etc.). Thevertical nanowires may be masked and etch utilizing a hard mask, thedrain and gate isolated, gate stacks (may be complementary) formed, andthe gates and dummy source may be isolated. The source can then beselectively etched out and replaced by a low-band-gap material to formthe hetero junction on top of a silicon channel enable a sharp junction.

ALD (Atomic Layer Deposition) and Spatial ALD (Spatial separation of thehalf-reactions) techniques may be utilized to form thin nearlymonocrystalline layers in a monolithic 3D fashion and for many of thevarious monolithic 3D structures disclosed herein and in theincorporated references. [S-ALD ref J. Vac. Sci. Technol. A 30(1),January/February 2012, Roll to Roll techniques form USA, Finland; andPoodt, P., et al., Advanced Materials 22 (2010) p. 3564]. These are lowtemperature processes that may be compatible with copper or aluminummetallization and/or low-k dielectrics on the layers below the ALD/S-ALDlayer being formed.

For example, the stacking of layers to eventually form a memory stack,may be formed by ALD/S-ALD exclusively or in combination with otherdeposition techniques such as low temp CVD. ALD/S-ALD may be utilized,for example, as described in at least incorporated reference U.S. Pat.No. 8,273,610 to form the p-Si 9906/oxide layers in FIG. 99C for FB-DRAMformation and devices, the RRAM stack of FIGS. 101D, 102D, 103F, 109D,110D, 192D, charge trap stacks such as FIG. 106F, and FIGS. 100D and200D for DRAM.

ALD layers may be doped in-situ with no need for thermal activation toform doped layers (and ultimately regions with masking and etchprocessing), and may be used to form both or one of the layers ofsemiconductor/dielectric stacks or semiconductor/semiconductor stacks,for example, Si & SiO₂, Ge & GeO, Si & Si of differing vertical dopantconcentrations and/or dopant types, etc. The ALD/S-ALD formed layers mayalso be conventionally doped with ion-implantation and activated withtechniques such as described in the incorporated references, forexample, with an optical anneal.

ALD/S-ALD may be utilized, for example, as described in at leastincorporated reference U.S. Pat. No. 8,273,610 to form an N+/N−/P+ stacksuch as shown in FIG. 26A to ultimately form horizontal transistors; maybe utilized top form the N+/P−/N+ layer stack of FIG. 39C to ultimatelyform vertical transistors; and may be utilized to form the layers 6802and 6803 of FIG. 68C to ultimately form RCAT transistors.

ALD/S-ALD may be utilized, for example, as described in at leastincorporated reference U.S. Pat. No. 8,273,610 to form the N+/P− stackof FIG. 137C to ultimately form an NVM FPGA configuration cell.

Also meta-material layers for thermal isolation layers, such asdisclosed in incorporated reference U.S. Patent Application 61/889,500may be formed with ALD/S-ALD techniques; disordered nanostructuredmaterials such as WSe2 and the nanoscale layered oxides such asSiO₂/Y₂O₃, SiO₂/Cr₂O₃, and SiO₂/Al₂O₃ for TIL 140.

ALD/S-ALD may be utilized, for example, for low temperature formation ofoxide layers, such as SiO₂, nearly crystalline silicon layers, andsilicon nitride layers such as Si₃N₄ and SiN. The formation of theselayers would not damage the underlying temperature sensitive layers andregions, for example, including copper, aluminum, low-k dielectrics.

Layer transfer a mono-crystalline layer of silicon on top of anunderlying layer or layers of interconnect metallization/dielectrics andtransistors/circuits allowing a relatively easy process to seed andcrystallize, such as by nanographioepitaxy, an overlying germanium layerwas disclosed in at least paragraph 134 of incorporated reference U.S.Pat. No. 8,273,610. This allows formation of the two types oftransistors with direct alignment to the underlying device layer.P-channel Ge transistors, such as, for example, an RCAT or MOSFET, maybe formed utilizing the technique in certain regions of the transferredlayer, and n-channel Si transistors, such as, for example, an RCAT orMOSFET, may be formed in the monocrystalline silicon of other regions ofthe layer transferred silicon layer. By utilizing the technique ofdoping and activating the layer to be transferred on the donor waferprior to transfer, a transistor such as, for example, an RCAT, may beformed on the transferred layer utilizing the methods of at least FIGS.66-68 and associated specification sections of incorporated referenceU.S. Pat. No. 8,273,610. The Ge regions may be crystallized prior to theformation of the silicon transistors and some common formation steps maybe taken advantage of, or the silicon based and Ge based transistors maybe formed in separate steps of the process flow. Si based MOSFETs may beformed, for example, by the gate replacement methods of at least FIGS.70, 81, 82 and associated specification sections of incorporatedreference U.S. Pat. No. 8,273,610. Regions of the silicon may be etchedout (leaving appropriate crystallized silicon edges, regions, spaces forthe graphioepitaxy and/or seeding) and crystallized Ge regions may beformed, and Ge based transistors made. Si based MOSFETs may be formed,for example, by the implant and optical anneal methods of at least FIGS.45, 46, 47 and associated specification sections of incorporatedreference U.S. Pat. No. 8,574,929. One of ordinary skill in the artwould recognize that there are many devices which may be formed above anunderlying layer or layers of interconnect metallization/dielectrics andtransistors/circuits wherein a portion of the transistors (such as butnot limited to the channel or portions of the transistor channel) may bemonocrystalline silicon based and a portion of the transistors (such asbut not limited to the channel or portions of the transistor channel)may be crystallized Ge based using a method or combination of methodsdisclosed herein and/or in the incorporated references. The Ge (or GaAs,InP, etc.) formed by LPE into subcritical vias of the transferredsilicon layer with engineered layer such as Ge—see at least FIGS. 27-28and associated specification sections of incorporated reference U.S.Pat. No. 8,574,929) transistor may be utilized for optical I/Os on thetop layer (or lower layers with optical passthrus above or below) of themonolithic 3D stack.

FIGS. 13A-13G illustrate an exemplary n-channel FD-MOSFET withintegrated TRL (Trap Rich Layer) and an exemplary process flow.Integrated TPS (Thermal Protective Structure), TIL (Thermal IsolationLayer), and/or TES (Thermally Enhanced Substrate) may be utilized tothermally protect the metallization, isolation layers, device electricalcharacteristics and reliability of devices that may reside in or on thesubstrate or a previously constructed layer in the 3D stack fromdamaging processes and processing temperatures. TPS, TIL and TESformation and composition details may be found in some of theincorporated references, for example, at least U.S. Patent Application61/889,500 and Ser. No. 14/298,917. An exemplary n-channel FD-MOSFETwith integrated TRL may be constructed in a 3D stacked layer utilizingprocedures outlined herein and in incorporated references. Forming theTRL on a donor wafer as part of the transferred layer may provide agreater process window for TRL formation, especially for temperatureexposures, than forming the TRL on the acceptor wafer, which may belimited to temperatures less than about 400° C. due to the presence ofcopper or aluminum metallization and low k IMDs on the layer or layersbelow the layer being processed.

Reasons for forming and utilizing a TRL layer and/or regions may includeRF applications, for example horizontal and/or vertical emf shielding.For example, RF transistor and circuit performance on any layer of a3DIC, such as a strata layer or base substrate, may be limited in termsof transmission line losses by the presence of parasitic surfaceconduction (PSC). A TRL layer would be considered effective if thepresence of the TRL provides an effective resistivity, the trueelectrical resistivity sensed by a co-planar waveguide (CPW) line,higher than about 1 kohm-cm, or higher than about 3 k-ohm-cm. This mayresult in a CPW attenuation versus frequency response that issubstantially similar to the response of a CPW on a quartz substrate. ATRL may accomplish this thru material or materials and processing thatcreates and/or incorporates defects in the material. A TRL may be formedwith temperature exposures and processes above about 400° C. when formedon a donor substrate prior to layer transfer, and may be formed bytemperature exposures and process of less than about 400° C. when formedon the acceptor wafer that may include copper or aluminum metallizationand/or low-k dielectrics, for example, prior to a monolithic 3D layertransfer or a TSV stack bonding step. An integrated TRL may provide ahigher performance for transistors and circuits built on thelayers/strata of a 3DIC system stack; for example, a radio frequency(RF) receiver/transmitter circuit may operate at greater than about 1gigahertz, a phase lock loop (PLL) circuit may operate at greater thanabout 1 megahertz, a Serializer/Deserializer (SerDes) circuit mayoperate at greater than about 1 gigahertz, an oscillator may have afrequency stability of better than 100 ppm/° C., an RF circuit mayexhibit ‘substrate’ losses when placed in a second (or third, etc.)layer/stratum of a monolithic 3DIC device which are, for example, lessthan 0.15 dB/mm at 2 GHz, less than 0.20 dB/mm at 4 GHz. The integratedTRL may provide a shielding effectiveness of vertically adjacentlayers/strata devices of, for example, more than 60 dB, more than 50 dB,or more than 70 dB.

As illustrated in FIG. 13A, SOI donor wafer substrate 1301 may includeback channel layer 1305 above Buried Oxide BOX layer 1303. Back channellayer 1305 may be doped by ion implantation and thermal anneal, mayinclude a crystalline material, for example, mono-crystalline (singlecrystal) silicon and may be heavily doped (greater than about 1e16atoms/cm³), lightly doped (less than about 1e16 atoms/cm³) or nominallyun-doped (less than about 1e14 atoms/cm³). SOI donor wafer substrate1301 may include a crystalline material, for example, mono-crystalline(single crystal) silicon and at least the upper layer near BOX layer1303 may be very lightly doped (less than about 1e15 atoms/cm³) ornominally un-doped (less than about 1e14 atoms/cm³). Back channel layer1305 may have additional ion implantation and anneal processing toprovide a different dopant level than SOI donor wafer substrate 1301 andmay have graded or various layers of doping concentration. SOI donorwafer substrate 1301 may have additional ion implantation and annealprocessing to provide a different dopant level than back channel layer1305 and may have graded or various layers of doping concentration. Thedonor wafer layer stack may alternatively be formed by epitaxiallydeposited doped or undoped silicon layers, or by a combination ofepitaxy and implantation, or by layer transfer. Annealing of implantsand doping may include, for example, conductive/inductive thermal,optical annealing techniques or types of Rapid Thermal Anneal (RTA orspike). The preferred at least top of SOI donor wafer substrate 1301doping will be undoped to eventually create an FD-MOSFET transistor withan undoped conduction channel. SOI donor wafer may be constructed bylayer transfer techniques described herein and/or incorporatedreferences or elsewhere as known in the art, or by laser annealed SIMOXat a post donor layer transfer to acceptor wafer step. BOX layer 1303may be thin enough to provide for effective DC or RF back and/ordevice/transistor body bias, for example, about 25 nm, or about 20 nm,or about 10 nm, or about 5 nm thick. Upper isolation layer 1332 may beformed by deposition of a dielectric such as, for example, siliconoxide, and/or by thermal/RTO oxidation of back channel layer 1305. Upperisolation layer 1332 may include, or may have below it, a layer (notshown) that may serve as a heat shield and/or conductive back plane, forexample, a layer of tungsten (similar to the description in FIGS. 39,40, 41, 42, 43 of U.S. Pat. No. 8,574,929 and U.S. patent applicationSer. No. 13/803,437). The thin layer of refractory metal with a highmelting point may be formed on top of the isolation layer and thenpatterned after layer transfer, thus forming metalized back-bias regionsfor the second layer of transistors, the back-bias region will not beharmed by the thermal cycles of the processing on the layer beingprocessed. Furthermore, back channel layer 1305 and Buried Oxide BOXlayer 1303 may be not formed and the transistor formation may proceedfrom a bulk donor substrate rather than an SOI based substrate.

Continuing with the FIG. 13A illustration, TRL 1340 may be formed on topof upper isolation layer 1332. Upper isolation layer 1332 may be etched(partially or fully) to form TRL regions (not shown).

TRL 1340 formation may include deposition of an amorphous silicon or apolysilicon film, or a combination of the two. The deposition mayutilize an LPCVD technique wherein the polycrystalline film may bedeposited at about 625° C. and the amorphous silicon film may bedeposited at about 525° C. Other techniques, such as sputtering, PECVD,etc., may be utilized. The deposited film may be partially crystallizedwith a rapid thermal anneal (RTA) exposure, for example about 100seconds at about 900° C. TRL 1340 may have a thickness that wouldaccomplish the effective resistivity metric at the frequency(ies) ofinterest for the circuit design discussed previously herein, and may be,for example, about 5 nm, about 10 nm, about 20 nm, about 30 nm, about 50nm about 100 nm, about 200 nm, or about 500 nm thick.

TRL 1340 formation may include damaging the surface and/or a top layerof, for example, back channel layer 1305 (or of the substrate in thecase of a bulk donor layer transfer method), thus creating a damagelayer (or regions if masked or etched). Damage may be caused by ionimplantation, for example, such as an Argon ion-implant of about 10¹⁵atoms/cm². Plasma sheath, or plasma source ion implantation may beutilized. Preferably the implantation is configured to damage and notdope the layer, the objective being to provide as high an effectiveresistivity as possible. The dose and energy may be set to bring thedamaged layer close to or completely amorphize the crystalline structureof the damaged layer or region.

TRL 1340 formation may include deposition of a silicon rich siliconoxide, a silicon rich silicon nitride, and may include deposition of asiliconoxynitride film. TRL 1340 formation may include deposition of acarbon or carbon rich film, for example, amorphous carbon, disorderedgrapheme, DLC (Diamond Like Carbon), disordered carbon nanotube mats, orSiCO. TRL 1340 formation may include some of the materials formed increation of the TIL layer of incorporated U.S. Patent Application61/889,500 that have a high trap density, for example, forming nanoscalelayered oxides or layers of disordered nanostructured materials.

Some references concerning trap layer mjateuails may be found in atleast these references: Frohman-Bentchkowsky, D. (1969). An integratedmetal-nitride-oxide-silicon (MNOS) memory. Proceedings of the IEEE,57(6), 1190-1192; and Frohman-Bentchkowsky, D., & Lenzlinger, M. (1969).Charge Transport and Storage in Metal-Nitride-Oxide-Silicon (MNOS)Structures. Journal of Applied Physics, 40(8), 3307-3319; and White, M.H., & Cricchi, J. R. (1972). Characterization of thin-oxide MNOS memorytransistors. Electron Devices, IEEE Transactions on, 19(12), 1280-1288;and Thermal and plasma nitridation of silicon and silicon dioxide forultrathin gate insulators of MOS VLSI. Ph.D. dissertation by Moslehi,Mehrdad Mahmud, Stanford University, 1986; Roda Neve, C., and Raskin, J.P. (2012). RF harmonic distortion of CPW lines on HR-Si and trap-richHR-Si substrates. Electron Devices, IEEE Transactions on, 59(4),924-932; and Sarafis, P., Hourdakis, E., Nassiopoulou, A. G., Roda Neve,C., Ben Ali, K., & Raskin, J. P. (2013). Advanced Si-based substratesfor RF passive integration: Comparison between local porous Si layertechnology and trap-rich high resistivity Si. Solid-State Electronics,87, 27-33; the following in their entirety are incorporated byreference. These references, esp. Moslehi's thesis, discuss variousprocesses, outside of ion implantation, which may be used to create anembedded layer of trapped charge, and characterize the trapped chargeper unit area as a function of various processing conditions.

TRL 1340 may be formed thicker than the desired end thickness, and thenthinned by, for example, CMP processing or etching, to the desired endthickness, or for the purposes of smoothing the surface to enableimproved bonding.

A pre-layer-transfer anneal may be performed as part of the TRL 1340formation process or after the formation of TRL 1340, and may include athermal anneal equal to or greater than the maximum temperature that theTRL 1340 would see during subsequent processing, for example, during the3D IC stack processing, including layer transfer/bonding,transistor/device formation, activation anneals, and so on. Thepre-layer-transfer anneal temperature may be about 10° C. greater thanthe process exposure maximum, or about 20° C. greater than the processexposure maximum, or about 30° C. greater than the process exposuremaximum, or about 40° C. greater than the process exposure maximum. Thepre-layer-transfer anneal temperature may be limited by theeffect/damage it may have on the doping gradients elsewhere in the donorstack, or the damage repair/stress/outgassing effects on TRL 1340, asexamples. The time of the pre-layer-transfer anneal at maximumtemperature (the process exposure maximum) may be less than about 130minutes, or less than about 1 hour, or less than about 2 hours. Theformation of TRL 1340 and/or the anneal of TRL 1340 and the donor stackmay be at a temperature and time greater than allowed by a metallizedacceptor structure, for example, above about 400° C., above about 600°C., above about 800° C., above about 1000° C.

As illustrated in FIG. 13B, the top surface of the donor wafer stackthat may include SOI donor wafer substrate 1301, may be prepared foroxide wafer bonding with a deposition of an oxide to form capping layer1329.

A layer transfer demarcation plane (shown as dashed line) 1399 may beformed by hydrogen implantation or other methods (such as a preformedSiGe layer) as described in the incorporated references, and may residewithin the SOI donor wafer substrate 1301. The SOI donor wafer substrate1301 stack surface 1382, and acceptor wafer 1397 (first shown in FIG.13C) may be prepared for wafer bonding as previously described in theincorporated references and may be low temperature (less thanapproximately 400° C.) bonded.

As illustrated in FIG. 13C, capping layer 1329, back channel layer 1305,BOX layer 1303 and remaining channel layer 1307 may be layer transferredto acceptor wafer 1397. Capping layer 1329 and acceptor wafer 1397 topbonding oxide (not shown) may be oxide to oxide bonded, thus forminglower isolation layer 1330. Acceptor wafer 1397, as described in theincorporated references and herein, may include, for example,transistors, circuitry, and metal, such as, for example, aluminum orcopper, interconnect wiring, a metal shield/heat sink layer or layers,and thru layer via metal interconnect strips or pads. Acceptor wafer1397 may be substantially comprised of a crystalline material, forexample mono-crystalline silicon or germanium, or may be an engineeredsubstrate/wafer such as, for example, an SOI (Silicon on Insulator)wafer or GeOI (Germanium on Insulator) substrate. Acceptor wafer 1397may include transistors such as, for example, MOSFETS, FD-MOSFETS,FinFets, FD-RCATs, BJTs, HEMTs, and/or HBTs. The portion of the SOIdonor wafer substrate 1301 that may be above (when the layer stack isflipped over and bonded to the acceptor wafer 1397) the layer transferdemarcation plane 1399 may be removed by cleaving or other lowtemperature processes as described in the incorporated references, suchas, for example, ion-cut with mechanical or thermal cleave or otherlayer transfer methods, thus forming remaining channel layer 1307.

Formation of transistors and devices on the layer being processed 1360without harming the underlying structures of acceptor wafer 1397 mayproceed with a variety of methods. For example, as disclosed in at leastFIGS. 33 and 46 and related specification sections of incorporated byreference U.S. Pat. No. 8,574,929, transistors may be formed with anintegrated heat shields and optical annealing. For example, formation ofCMOS in one transferred layer and the orthogonal connect stripmethodology may be found as illustrated in at least FIGS. 30-33, 73-80,and 94 and related specification sections of U.S. Pat. No. 8,273,610,and may be applied. Low temperature and/or heat shielded 3D stackingtransistor formation techniques may help preserve the effectiveness ofthe trap rich layer by not significantly annealing the defects andtraps.

The exemplary flow herein FIG. 13 is utilizing a similar transistorformation technique as described in incorporated U.S. Patent Application61/889,500, and may utilize a TIL, which may be integrated with TRL1340, on the top or bottom face of the TRL 1340, or both. Or may be onein the same—the TIL may also have trap properties of a TRL. Manyconventional semiconductor processing steps may now be utilized to formtransistors and devices on the layer being processed 1360 withoutharming the underlying structures of acceptor wafer 1397, for example, adeposition or anneal may be performed at 800° C. on layer beingprocessed 1360. Heat removal from the substrate, for example, such asvia a cooled chuck, is described in incorporated U.S. Patent Application61/889,500.

Damage/defects to a crystalline structure of back channel layer 1305 andremaining channel layer 1307 may be annealed by conventional thermalanneals with appropriate cold chuck equipment and/or some of theannealing methods as described in the incorporated references, forexample the short wavelength pulsed laser techniques, wherein the layerbeing processed 1360 (which may include back channel layer 1305, BOXlayer 1303 and remaining channel layer 1307) may be heated to defectannealing temperatures, but the underlying structures of acceptor wafer1397 may be kept below the damage temperature of acceptor wafer 1397,for example, less than about 400° C.

The top surface of remaining channel layer 1307 may be chemicallymechanically polished, and/or heat treated, to bring the surface qualityto conventional defect levels and/or may be thinned by low temperatureoxidation and strip processes, such as the TEL SPA tool radicaloxidation and HF:H₂O solutions as described in referenced patents andpatent applications. Thru the processing, the wafer sized layer channellayer 1307 could be thinned from its original total thickness, and itsfinal total thickness could be in the range of about 5 nm to about 20nm, for example, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, or 20 nm. Channellayer 1307 may have a thickness and/or doping that may allowfully-depleted channel operation when the FD-MOSFET transistor issubstantially completely formed. Acceptor wafer 1397 may include one ormore shield/heat sink layers 1318, which may include materials such as,for example, Aluminum, Tungsten (a refractory metal), copper, silicon orcobalt based silicides, or forms of carbon such as carbon nanotubes orgraphene, and may be layered itself as described herein FIG. 3 and in atleast incorporated U.S. Patent Application 61/889,500. Each shield/heatsink layer 1318 may have a thickness range of about 50 nm to about 1 mm,for example, 50 nm, 100 nm, 200 nm, 1300 nm, 500 nm, 0.1 um, 1 um, 2 um,and 10 um. Shield/heat sink layer 1318 may include isolation openingsalignment mark openings (not shown), which may be utilized for shortwavelength alignment of top layer (donor) processing to the acceptorwafer alignment marks (not shown). Shield/heat sink layer 1318 may actas a heat spreader. Electrically conductive materials may be used forthe two layers of shield/heat sink layer 1318 and thus may provide, forexample, a Vss and a Vdd plane and/or grid that may be connected to thedonor layer transistors above, as well may be connected to the acceptorwafer transistors below, and/or may provide below transferred layerdevice interconnection. Noise on the power grids, such as the Vss andVdd plane power conducting lines/wires, may be mitigated byattaching/connecting decoupling capacitors onto the power conductinglines of the grids. The decoupling caps, which may be within the secondlayer (donor, for example, donor wafer device structures) or first layer(acceptor, for example acceptor wafer transistors and devices 1302), mayinclude, for example, trench capacitors such as described by Pei, C., etal., “A novel, low-cost deep trench decoupling capacitor forhigh-performance, low-power bulk CMOS applications,” ICSICT (9^(th)International Conference on Solid-State and Integrated-CircuitTechnology) 2008, October 2008, pp. 1146-1149, of IBM. The decouplingcapacitors may include, for example, planar capacitors, such as poly tosubstrate or poly to poly, or MiM capacitors (Metal-Insulator-Metal).Shield/heat sink layer 1318 may include materials with a high thermalconductivity greater than 10 W/m-K, for example, copper (about 400W/m-K), aluminum (about 237 W/m-K), Tungsten (about 173 W/m-K), PlasmaEnhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD DLC (about1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene (about 5000W/m-K). Shield/heat sink layer 1318 may be sandwiched and/orsubstantially enclosed by materials with a low thermal conductivity(less than 10 W/m-K), for example, silicon dioxide (about 1.4 W/m-K).When there may be more than one shield/heat sink layer 1318 in thedevice, the heat conducting layer closest to the TRL 1340 may beconstructed with a different material, for example a high melting pointmaterial, for example a refractory metal such as tungsten, than theother heat conducting layer or layers, which may be constructed with,for example, a lower melting point material, for example such asaluminum or copper. The remaining SOI donor wafer substrate 1301 may nowalso be processed, such as smoothing and annealing, and reused foradditional layer transfers. Upper isolation layer 1332 and/or lowerisolation layer 1330 may include thicknesses of less than about 1 um,less than about 500 nm, less than about 400 nm, less than about 300 nm,less than about 200 nm, or less than about 100 nm.

As illustrated in FIG. 13D, transistor and back channel isolationregions 1385 and/or transistor isolation regions 1387 may be formed.Transistor isolation region 1387 may be formed by mask defining andplasma/RIE etching channel layer 1307, substantially to the top of BOXlayer 1303 (not shown), substantially into BOX layer 1303, or backchannel layer 1305 (not shown). Transistor and back channel isolationregions 1385 and transistor-backchannel-TRL isolation regions 1386 maybe formed by mask defining and plasma/RIE etching channel layer 1307,BOX layer 1303 and back channel layer 1305, substantially to the top ofupper isolation layer 1332 (not shown) or substantially into upperisolation layer 1332 for transistor and back channel isolation regions1385 and substantially to lower isolation layer 1330 fortransistor-backchannel-TRL isolation regions 1386. Note:transistor-backchannel-TRL isolation regions 1386 are utilized when theelectrical conductivity of the TRL 1340 is undesirably high and maycause undesired leakage paths between the eventual TLVs. Thus channelregion 1323 may be formed, which may substantially form the transistorbody, back-channel region 1321 may be formed, which may provide a backbias and/or Vt control by doping or bias to one or more channel regions1323, and BOX region 1331. (TRL regions 1341 may also be thusly formed.)Back-channel region 1321 may be ion implanted for Vt control and/or bodybias efficiency. A conventional or low-temperature gap fill dielectric,such as SACVD oxide, may be deposited and chemically mechanicallypolished, the oxide remaining in transistor and back channel isolationregions 1385 and transistor isolation regions 1387. An optical or aconventional thermal and/or oxidizing anneal may be performed to annealetch damage in back-channel region 1321 and channel region 1323, anddensify the STI oxide in transistor and back channel isolation regions1385 and transistor isolation regions 1387. The doping concentration ofchannel region 1323 may include vertical or horizontal gradients ofconcentration or layers of differing doping concentrations. The dopingconcentration of back-channel region 1321 may include vertical orhorizontal gradients of concentration or layers of differing dopingconcentrations. Any additional doping, such as ion-implanted channelimplants, may be activated and annealed with optical annealing, orconventionally. BOX region 1331 may be a relatively thin dielectric,including the thickness range of about 5 nm to about 100 nm, at least aportion of which being between the back-channel region 1321 and channelregion 1323. Back-channel region 1321 could be constructed from amaterial other than crystalline silicon, for example, a refractory metalor doped silicon in crystallized form, poly or amorphous, or otherconductive materials that are acceptable for semiconductor processingand can withstand high temperatures.

As illustrated in FIG. 13E, a transistor forming process, such as aconventional HKMG with raised source and drains (S/D), may be performed.For example, a dummy gate stack (not shown), utilizing oxide andpolysilicon, may be formed, gate spacers 1351 may be formed, raised S/Dregions 1353 and channel stressors may be formed by etch and epitaxialdeposition, for example, of SiGe and/or SiC/P depending on P or Nchannel (and may be doped in-situ or ion-implantation and annealactivation), LDD and S/D ion-implantations may be performed, and firstILD 1355 may be deposited and CMP′d to expose the tops of the dummygates. Thus transistor channel region 1325 and S/D & LDD regions 1357may be formed. The dummy gate stack may be removed and a gate dielectric1359 may be formed and a gate metal material gate electrode 1361,including a layer of proper work function metal (Ti_(x)Al_(y),N_(z) forexample) and a conductive fill, such as aluminum, and may be depositedand CMP′d. The gate dielectric 1359 may be an atomic layer deposited(ALD) gate dielectric that may be paired with a work function specificgate metal in the industry standard high k metal gate process schemes,for example, as described in the incorporated references. Furthermore,the gate dielectric on transistors may have different dielectricpermittivities than silicon dioxde. The gate dielectric permittivity ofthe second layer transistors may be different than the gate dielectricpermittivity of the first layer transistors. An optical anneal may beperformed to densify and/or remove defects from gate dielectric 1359,anneal defects and activate dopants such as LDD and S/D implants,densify the first ILD 1355, form DSS junctions (Dopant SegregatedSchottky such as NiSi₂), and/or form contact and S/D silicides (notshown). Optionally, portions of transistor isolation region 1387 and BOXregion 1331 may be lithographically defined and etched away, thusforming second transistor isolation regions 1389 and PD transistor area1363. Partially depleted transistors (not shown) may be constructed in asimilar manner as the FD-MOSFETs constructed on transistor channelregion 1325 herein, but now with the thicker back-channel region 1321silicon as its channel body. PD transistor area 1363 may also beutilized to later form a direct connection thru a contact to theback-channel region 1321 for back bias and Vt control of the transistorwith transistor channel region 1325. This may also be utilized for RFtransistors. If no PD devices are desired, then it may be more efficientto later form a direct connection thru a contact to the back-channelregion 1321 for back bias and Vt control of the transistor withtransistor channel region 1325 by etching a contact thru transistorisolation region 1387.

As illustrated in FIG. 13F, a thick oxide 1363 may be deposited andplanarized. Source, gate, drain, two types of back contact openings maybe masked, etched, and filled with electrically conductive materialspreparing the transistors to be connected via metallization. Thus gatecontact 1365 connects to gate electrode 1361, source & drain contacts1366 connect to raised S/D regions 1353, back channel contact 1368 mayconnect to back-channel region 1321, and direct back contact 1367 mayconnect to back-channel region 1321. Back channel contact 1368 anddirect back contact 1367 may be formed to connect to shield/heat sinklayer 1318 by further etching, and may be useful for hard wiring a backbias that may be controlled by, for example, the second layer or firstlayer transistors and circuitry into the FD MOSFET.

As illustrated in FIG. 13G, thru layer vias (TLVs) 1380 may be formed byetching thick oxide 1363, first ILD 1355, transistor-backchannel-TRLisolation regions 1386, upper isolation layer 1332, lower isolationlayer 1330, and filling with an electrically and thermally conductingmaterial (such as tungsten or cooper) or an electrically non-conductingbut thermally conducting material (such as described herein and in theincorporated references). Second device layer metal interconnect 1381may be formed by conventional processing. TLVs 1380 may be constructedof thermally conductive but not electrically conductive materials, forexample, DLC (Diamond Like Carbon), and may connect the FD-MOSFETtransistor device and other devices on the top (second) crystallinelayer thermally to shield/heat sink layer 1318. TLVs 1380 may beconstructed out of electrically and thermally conductive materials, suchas Tungsten, Copper, or aluminum, and may provide a thermal andelectrical connection path from the FD-MOSFET transistor device andother devices on the top (second) crystalline layer to shield/heat sinklayer 1318, which may be a ground or Vdd plane in the design/layout.TLVs 1380 may be also constructed in the device scribelanes(pre-designed in base layers or potential dicelines) to provide thermalconduction to the heat sink, and may be sawed/diced off when the waferis diced for packaging, not shown). Shield/heat sink layer 1318 may beconfigured to act (or adapted to act) as an emf (electro-motive force)shield to prevent direct layer to layer cross-talk between transistorsin the donor wafer layer and transistors in the acceptor wafer. Inaddition to static ground or Vdd biasing, shield/heat sink layer 1318may be actively biased with an anti-interference signal from circuitryresiding on, for example, a layer of the 3D-IC or off chip. The formedFD-MOSFET transistor device may include semiconductor regions whereinthe dopant concentration of neighboring regions of the transistor in thehorizontal plane, such as traversed by exemplary dopant plane 1384, mayhave regions, for example, transistor channel region 1325 and S/D & LDDregions 1357, that differ substantially in dopant concentration, forexample, a 10 times greater doping concentration in S/D & LDD regions1357 than in transistor channel region 1325, and/or may have a differentdopant type, such as, for example p-type or n-type dopant, and/or may bedoped and substantially undoped in the neighboring regions. For example,transistor channel region 1325 may be very lightly doped (less thanabout 1e15 atoms/cm³) or nominally un-doped (less than about 1e14atoms/cm³) and S/D & LDD regions 1357 may be doped at greater than about1e15 atoms/cm³ or greater than about 1e16 atoms/cm³. For example,transistor channel region 1325 may be doped with p-type dopant and S/D &LDD regions 1357 may be doped with n-type dopant.

An operations thermal conduction path may be constructed from thedevices in the upper layer, the transferred donor layer and formedtransistors, to the acceptor wafer substrate and an associated heatsink. The thermal conduction path from the FD-MOSFET transistor deviceand other devices on the top (second) crystalline layer, for example,raised S/D regions 1353, to the acceptor wafer heat sink (not shown, butmay be placed on the backside of substrate 1300, may include source &drain contacts 1366, second device layer metal interconnect 1381, TLV1380, a portion of heat sink/shield 1318, 1308, 1312, 1314, and acceptorsubstrate 1300. The elements of the thermal conduction path may includematerials that have a thermal conductivity greater than 10 W/m-K, forexample, copper (about 400 W/m-K), aluminum (about 237 W/m-K), andTungsten (about 173 W/m-K), and may include material with thermalconductivity lower than 10 W/m-K but have a high heat transfer capacitydue to the wide area available for heat transfer and thickness of thestructure (Fourier's Law), such as, for example, acceptor substrate1300. The elements of the thermal conduction path may include materialsthat are thermally conductive but may not be substantially electricallyconductive, for example, Plasma Enhanced Chemical Vapor DepositedDiamond Like Carbon-PECVD DLC (about 1000 W/m-K), and Chemical VaporDeposited (CVD) graphene (about 5000 W/m-K). The acceptor waferinterconnects may be substantially surrounded by BEOL isolation 1310,which may be a dielectric such as, for example, carbon doped siliconoxides. The heat removal apparatus, which may include acceptor waferheat sink (not shown), may include an external surface from which heattransfer may take place by methods such as air cooling, liquid cooling,or attachment to another heat sink or heat spreader structure.

Furthermore, some or all of the layers utilized as shield/heat sinklayer 1318, which may include shapes of material such as the strips orfingers as illustrated in at least FIG. 33B and related specificationsections of U.S. Pat. No. 8,450,804, may be driven by a portion of thesecond layer transistors and circuits (within the transferred donorwafer layer or layers) or the acceptor wafer transistors and circuits,to provide a programmable back-bias to at least a portion of the secondlayer transistors. The programmable back bias may utilize a circuit todo so, for example, such as shown in FIG. 17B of U.S. Pat. No.8,273,610, the contents incorporated herein by reference; wherein the‘Primary’ layer may be the second layer of transistors for which theback-bias is being provided, the ‘Foundation’ layer could be either thesecond layer transistors (donor) or first layer transistors (acceptor),and the routing metal lines connections 1723 and 1724 may includeportions of the shield/heat sink layer 1318 layer or layers. Moreover,some or all of the layers utilized as shield/heat sink layer 1318, whichmay include strips or fingers as illustrated in FIG. 33B and relatedspecification of U.S. Pat. No. 8,450,804, may be driven by a portion ofthe second layer transistors and circuits (within the transferred donorwafer layer or layers) or the acceptor wafer transistors and circuits toprovide a programmable power supply to at least a portion of the secondlayer transistors. The programmable power supply may utilize a circuitto do so, for example, such as shown in FIG. 17C of U.S. Pat. No.8,273,610, the contents incorporated herein by reference; wherein the‘Primary’ layer may be the second layer of transistors for which theprogrammable power supplies are being provided to, the ‘Foundation’layer could be either the second layer transistors (donor) or firstlayer transistors (acceptor), and the routing metal line connectionsfrom Vout to the various second layer transistors may include portionsof the shield/heat sink layer 1318 layer or layers. The Vsupply on line17C12 and the control signals on control line 17C16 may be controlled byand/or generated in the second layer transistors (for example donorwafer device structures such as the FD-MOSFETs formed as described inrelation to FIG. 13) or first layer transistors (acceptor, for exampleacceptor wafer transistors and devices 1302), or off chip circuits.Furthermore, some or all of the layers utilized as shield/heat sinklayer 1318, which may include strips or fingers as illustrated in FIG.33B and related specification of U.S. Pat. No. 8,450,804 or other shapessuch as those in FIG. 33B, may be utilized to distribute independentpower supplies to various portions of the second layer transistors orfirst layer transistors (acceptor, for example acceptor wafertransistors and devices 1302) and circuits; for example, one powersupply and/or voltage may be routed to the sequential logic circuits ofthe second layer and a different power supply and/or voltage routed tothe combinatorial logic circuits of the second layer. Moreover, thepower distribution circuits/grid may be designed so that Vdd may have adifferent value for each stack layer. Patterning of shield/heat sinklayer 1318 or layers can impact their heat-shielding capacity. Thisimpact may be mitigated, for example, by enhancing the top shield/heatsink layer 1318 areal density, creating more of the secondaryshield/heat sink layers 1318, or attending to special CAD rulesregarding their metal density, similar to CAD rules that are required toaccommodate Chemical-Mechanical Planarization (CMP). These constraintswould be integrated into a design and layout EDA tool. Moreover, thesecond layer of circuits and transistors, for example, for example donorwafer device structures such as the FD-MOSFETs formed as described inrelation to FIG. 13, may include I/O logic devices, such as SerDes(Serialiser/Deserialiser), and conductive bond pads (not shown). Theoutput or input conductive pads of the I/O circuits may be coupled, forexample by bonded wires, to external devices. The output or inputconductive pads may also act as a contact port for the 3D device outputto connect to external devices. The emf generated by the I/O circuitscould be shielded from the other layers in the stack by use of, forexample, the shield/heat sink layer 1318. Placement of the I/O circuitson the same stack layer as the conductive bond pad may enable closecoupling of the desired I/O energy and lower signal loss. Furthermore,the second layer of circuits and transistors, for example donor waferdevice structures such as the FD-MOSFETs formed as described in relationto FIG. 13, may include RF (Radio Frequency) circuits and/or at leastone antenna. For example, the second layer of circuits and transistorsmay include RF circuits to enable an off-chip communication capabilityto external devices, for example, a wireless communication circuit orcircuits such as a Bluetooth protocol or capacitive coupling. The emfgenerated by the RF circuits could be shielded from the other layers inthe stack by use of, for example, the TRL 1340 and/or shield/heat sinklayer 1318.

TLVs 1380 may be formed through the transferred layers. As thetransferred layers may be thin, on the order of about 1 um or less inthickness, the TLVs may be easily manufactured as a typical metal tometal via may be, and said TLV may have state of the art diameters suchas nanometers or tens to a few hundreds of nanometers, such as, forexample about 250 nm or about 100 nm or about 50 nm. The thinner thetransferred layers, the smaller the thru layer via diameter obtainable,which may result from maintaining manufacturable via aspect ratios. Thethickness of the layer or layers transferred according to someembodiments of the invention may be designed as such to match and enablethe most suitable obtainable lithographic resolution (and enable the useof conventional state of the art lithographic tools), such as, forexample, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidthresolution and alignment capability, such as, for example, less thanabout 5 nm, 10 nm, 20 nm, or 40 nm alignment accuracy/precision/error,of the manufacturing process employed to create the thru layer vias orany other structures on the transferred layer or layers. Design choicesmay determine if TLVs are formed thru transistor and back channelisolation regions 1385 and/or thru transistor-backchannel-TRL isolationregions 1386.

Formation of CMOS in one transferred layer and the orthogonal connectstrip methodology may be found as illustrated in at least FIGS. 30-33,73-80, and 94 and related specification sections of U.S. Pat. No.8,273,610, and may be applied to at least the FIG. 13 formationtechniques herein. Transferred layer or layers may have regions of STIor other transistor elements within it or on it when transferred, butwould then use alignment and connection schemes for layer transfer ofpatterned layers as described in incorporated patent references.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 13A through 13G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, a p-channel FD-MOSFET maybe formed with changing the types of dopings appropriately. Moreover,the SOI donor wafer substrate 1301 may be n type or un-doped.Furthermore, transistor and back channel isolation regions 1385 andtransistor isolation region 1387 may be formed by a hard mask definedprocess flow, wherein a hard mask stack, such as, for example, siliconoxide and silicon nitride layers, or silicon oxide and amorphous carbonlayers, may be utilized. Moreover, CMOS FD MOSFETs may be constructedwith n-MOSFETs in a first mono-crystalline silicon layer and p-MOSFETsin a second mono-crystalline layer, which may include differentcrystalline orientations of the mono-crystalline silicon layers, such asfor example, <100>, <111> or <551>, and may include different contactsilicides for optimum contact resistance to p or n type source, drains,and gates. Further, dopant segregation techniques (DST) may be utilizedto efficiently modulate the source and drain Schottky barrier height forboth p and n type junctions formed. Furthermore, raised source and draincontact structures, such as etch and epi SiGe and SiC, may be utilizedfor strain and contact resistance improvements and the damage from theprocesses may be optically annealed. Strain on a transistor channel toenhance carrier mobility may be accomplished by a stressor layer orlayers as well. Moreover, a process could be done on bulk donor waferrather than an SOI wafer as well to form other types of transistorswithout integrated body/back-channel layer/regions. Additionally, thelayer transfer process may utilize a method other than ion-cut, forexample, a porous layer or selectively etchable layer, detach layermethod. Furthermore, a process could be done to form other types oftransistors on the layer to be processed 1360, for example, FinFets orTFETs. Many other modifications within the scope of the invention willsuggest themselves to such skilled persons after reading thisspecification. Thus the invention is to be limited only by the appendedclaims.

A donor wafer that may include a pre-made TRL and other layers, forexample, the structure as illustrated in FIG. 13B, may be manufacturedfor/by and supplied by a wafer vendor such as MEMC/SunEdison, SEH,Soitec, etc.

A donor wafer that may include a pre-made TRL and other layers, forexample, the structure as illustrated in FIG. 13B, may be layertransferred utilized the perforated carrier wafer methods as describedin at least FIGS. 184, 185, 186, and 187 and related specificationsections of U.S. Pat. No. 8,273,610. A debond/release etchant protectlayer may be included in the transfer layer stack to protect the TRL1340 and other layers from the debond/release etchant utilized in theperforated carrier wafer methodology.

A TRL may be formed directly on the acceptor wafer prior to a layertransfer of the material to form the next layer of devices and circuits.Structures and devices similar to those described and illustrated withrespect to at least FIG. 13 may be formed, but the TRL formation may belimited to temperatures less than about 400° C. due to the presence ofcopper or aluminum metallization and low k IMDs on the layer or layersbelow the layer being processed. An exemplary process flow is describedwith respect to FIGS. 14A-14E. FIG. 14E illustrates an exemplaryn-channel FD-MOSFET with integrated TRL (Trap Rich Layer). IntegratedTPS (Thermal Protective Structure), TIL (Thermal Isolation Layer),and/or TES (Thermally Enhanced Substrate) may be utilized to thermallyprotect the metallization, isolation layers, device electricalcharacteristics and reliability of devices that may reside in or on thesubstrate or a previously constructed layer in the 3D stack fromdamaging processes and processing temperatures. Formation andcomposition details may be found in at least some of the incorporatedreferences, for example, U.S. Patent Application 61/889,500 and Ser. No.14/298,917. An exemplary n-channel FD-MOSFET with integrated TRL may beconstructed in a 3D stacked layer utilizing procedures outlined hereinand in incorporated references.

As illustrated in FIG. 14A, SOI donor wafer substrate 1401 may includeback channel layer 1405 above Buried Oxide BOX layer 1403. Back channellayer 1405 may be doped by ion implantation and thermal anneal, mayinclude a crystalline material, for example, mono-crystalline (singlecrystal) silicon and may be heavily doped (greater than about 1e16atoms/cm³), lightly doped (less than about 1e16 atoms/cm³) or nominallyun-doped (less than about 1e14 atoms/cm³). SOI donor wafer substrate1401 may include a crystalline material, for example, mono-crystalline(single crystal) silicon and at least the upper layer near BOX layer1403 may be very lightly doped (less than about 1e15 atoms/cm³) ornominally un-doped (less than about 1e14 atoms/cm³). Back channel layer1405 may have additional ion implantation and anneal processing toprovide a different dopant level than SOI donor wafer substrate 1401 andmay have graded or various layers of doping concentration. SOI donorwafer substrate 1401 may have additional ion implantation and annealprocessing to provide a different dopant level than back channel layer1405 and may have graded or various layers of doping concentration. Thedonor wafer layer stack may alternatively be formed by epitaxiallydeposited doped or undoped silicon layers, or by a combination ofepitaxy and implantation, or by layer transfer. Annealing of implantsand doping may include, for example, conductive/inductive thermal,optical annealing techniques or types of Rapid Thermal Anneal (RTA orspike). The preferred at least top of SOI donor wafer substrate 1401doping will be undoped to eventually create an FD-MOSFET transistor withan updoped conduction channel. SOI donor wafer may be constructed bylayer transfer techniques described herein or elsewhere as known in theart, or by laser annealed SIMOX at a post donor layer transfer toacceptor wafer step. BOX layer 1403 may be thin enough to provide foreffective DC or RF back and/or device/transistor body bias, for example,about 25 nm, or about 20 nm, or about 10 nm, or about 5 nm thick.Furthermore, back channel layer 1405 and Buried Oxide BOX layer 1403 maybe not formed and the transistor formation may proceed from a bulk donorsubstrate rather than an SOI based substrate.

As illustrated in FIG. 14B, the top surface of the donor wafer stackthat may include SOI donor wafer substrate 1401, may be prepared forwafer bonding with a deposition of an oxide on or by thermal/RTOoxidation of back channel layer 1405 to form bonding oxide layer 1471.Bonding oxide layer 1471 may include, or may have below it, a layer (notshown) that may serve as a heat shield and/or conductive back plane, forexample, a layer of tungsten (a layer of tungsten (similar to thedescription in FIGS. 39, 40, 41, 42, 43 of U.S. Pat. No. 8,574,929 andU.S. patent application Ser. No. 13/803,437). The thin layer ofrefractory metal with a high melting point may be formed on top of theisolation layer and then patterned after layer transfer, thus formingmetalized back-bias regions for the second layer of transistors, theback-bias region will not be harmed by the thermal cycles of theprocessing on the layer being processed.

A layer transfer demarcation plane (shown as dashed line) 1499 may beformed by hydrogen implantation or other methods as described in theincorporated references, and may reside within the SOI donor wafersubstrate 1401.

As illustrated in FIG. 14C, acceptor substrate 1497 may be prepared anda TRL 1440 may be formed including a capping/bonding layer 1431.Acceptor substrate 1497 may be prepared in a similar manner as at leastas the structures and devices described in FIGS. 1A-1E of incorporatedU.S. Patent Application 61/889,500, up to and including lower isolationlayer 1300 (lower isolation layer 1430 in FIG. 14C), and using known inthe art techniques. Acceptor wafer 1497, as described in theincorporated references and herein, may include, for example,transistors, circuitry, and metal, such as, for example, aluminum orcopper, interconnect wiring, a metal shield/heat sink layer or layers,and thru layer via metal interconnect strips or pads. Acceptor wafer1497 may be substantially comprised of a crystalline material, forexample mono-crystalline silicon or germanium, or may be an engineeredsubstrate/wafer such as, for example, an SOI (Silicon on Insulator)wafer or GeOI (Germanium on Insulator) substrate. Acceptor wafer 1497may include transistors such as, for example, MOSFETS, FD-MOSFETS,FinFets, FD-RCATs, BJTs, HEMTs, and/or HBTs.

TPS protective structures to protect the desired regions of substratedevices may be constructed. These protective structures may beconstructed using conventional and known in the art processingtechniques. A substrate 1400, for example, a monocrystalline siliconwafer which may be thermally enhanced (a Thermally EnhancedSubstrate—TES—as described in incorporated U.S. Patent Application61/889,500), of which a portion is shown in FIG. 14, may have substratedevice regions 1402 including devices, such as, for example,transistors, capacitors, and resistors. These substrate device regions1402 could be formed as eventual product dice with surroundingscribelanes and die edge seals. The devices within the regions ofsubstrate devices could be wholly or partially within the substrate 1400material. The scribelanes may also be called dicing streets orscribelines.

The substrate 1400 may also have a backside surface 1404 that may beutilized to conduct processing heat (the heat source may be the layerbeing processed 1460 during device formation steps or portions of theequipment performing the processing such as IR lamps) from the substrate1400 to a processing equipment cooling chuck or other thermalconduction/heat removal device, generally within the processingequipment.

The substrate device regions 1402 may have corresponding regions ofsubstrate metallization 1408 and BEOL isolation 1410 interconnectlayers, which may include copper or aluminum metallization materials andlow-k dielectric inter-metal dielectrics (IMD) respectively. These maybe constructed with known in the art BEOL processing.

As part of the construction of or separately from the formation ofregions of substrate metallization 1408 and BEOL isolation 1410interconnect layers, one or more shield layer or regions 1418 ofmetallization and isolation may be constructed. Details are inreferenced applications. For example, the shield layer or regions 1418metallization may include materials such as tungsten, copper, aluminum,grapheme, diamond, carbon, materials with a high thermal conductivity(>10 W/m-K) and an appropriate melting/softening point. The shield layeror regions 1418 may be constructed as a continuous slab acrosssubstantially the entire extant of the substrate area, or may be formedas regions.

The shield layer or regions 1418 may have terminations within the devicedie scribelanes. The shield layer or regions 1418 may include TLVlanding pads wherein signals from the second layer of devices mayconnect either to a lower shield layer (for example shield layer orregions 1418) or to the interconnect layers or regions of substratemetallization 1408 and BEOL isolation 1410 interconnect or lower layerdevices and circuits. The shield layer or regions 1418 may be thermallybut not electrically connected or may be thermally and electricallyconnected to the substrate 1400 in a variety of ways.

The scribelanes, for example, scribelane with thermal via stacks andcontinuous shield 1420 and/or scribelane with thermal via stacks and cutshield layer 1422, may be substantially populated with thermal viastacks, which may be formed as thermal via stacks with via landing pads1412 as each metallization and via layer of the regions of substratemetallization 1408 and BEOL isolation 1410 interconnect layers areformed, or the thermal vias in the scribelane 1414 may be formed as anetched and filled deep-via prior to the formation of the shield layer orregions 1418. Forming the thermal via stack after the regions ofsubstrate metallization 1408 and BEOL isolation 1410 interconnect layersare formed may provide the use of a different BEOL isolation material,material that may be more thermally isolative and/or thermally stable,for the thermal via stacks than for the devices. The thermal vias in thescribelane 1414 may also be formed as one or a few to substantially fill(with appropriate stress relief structures) the scribelane with metal(thermally conductive) material (as much as practical given CMP dishingdesign rules) that may be part of the shield layer formation, or may beformed in a separate metal deposition and planarization step and mayprovide use of a more thermally conductive material than copper oraluminum to form the thermal vias in the scribelane 1414, for example,carbon nanotubes, Plasma Enhanced Chemical Vapor Deposited Diamond LikeCarbon-PECVD DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD)graphene (about 5000 W/m-K).

As dictated by design choices, the thermal vias (such as, for example,substantially all or a portion of thermal via stacks with via landingpads 1412 and/or thermal vias in the scribelane 1414, and/or in-diethermal via stacks 1416 and/or fill-in thermal paths 1417) may truncatein a dielectrically isolated or reverse biased junction electricallyisolated connection to the substrate, or the thermal vias may truncateas a conventional forward biased junction or no junction substratecontact that may be thermally and electrical connected to the substrate.Processing, structure, and operational details are in referencedapplications.

In-die thermal via stacks 1416 (may also be called in-die thermal viapaths) may also be constructed over the regions of substrate devices1402 (within die extant 1424) by forming a via stack that utilizes theinterconnect structures of the regions of substrate metallization 1408and BEOL isolation 1410 interconnect layers, with a via connection 1419from the shield layer to a metallization layer/segment within theregions of substrate metallization 1408 and BEOL isolation 1410interconnect layers. Via connection 1419 may be connected at a laterstep to electrically couple to the second layer devices (such as a TLV),or may primarily enable (as part of a thermal path) a thermal connectionfrom substrate 1400 to shield layer or regions 1418. Details of thisformation have been described in referenced applications.

Additionally, as a matter of design choice and may be controlled by anEDA design and placement algorithm, fill-in thermal paths 1417 may beadded to a chip die design/layout to maximize local and die averagethermal conductivity. The fill-in thermal paths 1417 may be formedanywhere on the die and from any level of the regions of substratemetallization 1408 and BEOL isolation 1410 interconnect layers to thesubstrate 1400, for example, metal 4 to substrate, metal 3 to substrate,and so on). Fill-in thermal paths 1417 may be added to a power or groundline as extra thermal connections to the substrate 1400, which may beelectrically conductive or non-conductive due to design constraints.Fill-in thermal paths 1417 may be additional connections beyond what aconventional design or EDA tool may provide/construct. Fill-in thermalpaths 1417 may be added to/formed in so called ‘white space’ within thedevice die, where there may be a path vertically and horizontally thruthe regions of substrate metallization 1408 and BEOL isolation 1410interconnect layers to the substrate 1400. Moreover, fill-in thermalpaths 1417 may be formed from the CMP fill structures of one or more ofthe regions of substrate metallization 1408 and BEOL isolation 1410interconnect layers.

As a matter of design choice, die seal 1406 (or die seal-ring) may beutilized as a thermal connection from either interconnect metal layersof the ring itself or the shield layer or regions 1418 to the substrate1400.

Lower isolation layer 1430 may be deposited on top of shield layer orregions 1418 to protect and electrically and partially thermally isolateabove and below and may include the bonding oxides for an ion-cut layertransfer process (for the case wherein TRL 1440 is formed on a donorwafer or substrate). Lower isolation layer 1430 may include designed-invoids (not shown), for example, by etch removal of portions of lowerisolation layer 1430, thus forming regions of vacuum and/or gas andregions of the remaining material (for example, silicon oxide) of lowerisolation layer 1430. The voids may be formed such that they extendfully or partially thru the entire thickness lower isolation layer 1430.The presence of the voids may reduce the average thermal conductivity oflower isolation layer 1430. The voids may include greater than about 5%,greater than about 10%, greater than about 20%, or greater than about50% of the area and/or volume of lower isolation layer 1430, thusaffecting the total average lower isolation layer 1430 thermalconductivity by greater than about 5%, or greater than about 50%.

Continuing with the FIG. 14C illustration, TRL 1440 may be formed on topof lower isolation layer 1430. TRL 1440 may be etched (partially orfully) to form TRL regions (not shown).

TRL 1440 formation may include deposition of an amorphous silicon or apolysilicon film, or a combination of the two. The deposition mayutilize deposition techniques and processes that will not thermally harmthe underlying metallization and/or dielectric BEOL isolation materialsand structure, which for copper and/or aluminum metallization and low-kdielectrics are generally less than 400° C. temperature exposures.Techniques, such as sputtering, PECVD, etc., may be utilized. TRL 1440may have a thickness that would accomplish the effective resistivitymetric at the frequency(ies) of interest for the circuit design asdiscussed previously herein, and may be, for example, about 5 nm, about10 nm, about 20 nm, about 30 nm, about 50 nm about 100 nm, about 200 nm,or about 500 nm thick.

TRL 1440 formation may include damaging the surface and a top layer of,for example, a deposited layer of silicon or a layer transferred siliconlayer, or of lower isolation layer 1430, thus creating a damage layer(or regions if masked or etched) Damage may be caused by ionimplantation, for example, such as an Argon ion-implant of about 10¹⁵atoms/cm². Plasma sheath, or plasma source ion implantation may beutilized. Preferably the implantation is configured to damage and notdope the layer, the objective being to provide as high an effectiveresistivity as possible. The dose and energy may be set to bring thedamaged layer close to or completely amorphize the crystalline structureof the damaged layer or region.

TRL 1440 formation may include deposition of a silicon rich siliconoxide, a silicon rich silicon nitride, and may include deposition of asiliconoxynitride film. TRL 1440 formation may include deposition of acarbon or carbon rich film, for example, amorphous carbon, disorderedgrapheme, DLC (Diamond Like Carbon), disordered carbon nanotube mats, orSiCO. TRL 1440 formation may include some of the materials formed increation of the TIL layer of incorporated U.S. Patent Application61/889,500 that have a high trap density, for example, forming nanoscalelayered oxides or layers of disordered nanostructured materials.

TRL 1440 may be formed thicker than the desired end thickness, and thenthinned by, for example, CMP processing or etching, to the desired endthickness, or for the purposes of smoothing the surface to enableimproved bonding.

A pre-layer-transfer anneal may be performed as part of the TRL 1440formation process or after the formation of TRL 1440, and may include athermal anneal equal to or greater than the maximum temperature that theTRL 1440 would see during subsequent processing, for example, during the3D IC stack processing, including layer transfer/bonding,transistor/device formation, activation anneals, and so on as long asthe TRL formation temperature does not exceed the damage temperature ofunderlying structures, which may be less than about 400° C., or lessthan about 350° C., for copper and low-k BEOL materials and structures.If higher temperature metals and dielectrics are utilized in theconstruction of the acceptor substrate 1497, for example, tungsten andsilicon dioxide, greater temperatures to form the TRL 1440 may beavailable. The ramp up and cool down rates may be carefully controlleddepending on the type and condition of material in TRL 1440 to minimizecracking, outgassing effects, and other stress effects on the stack. Thetime of the pre-layer-transfer anneal at maximum temperature (theprocess exposure maximum) may be less than about 30 minutes, or lessthan about 1 hour, or less than about 2 hours.

Continuing as illustrated in FIG. 14C, the top surface of the donorwafer stack that may include acceptor substrate 1497, may be preparedfor oxide wafer bonding with a deposition of a low temperature oxide toform capping/bonding layer 1431.

The SOI donor wafer substrate 1401 stack, such as surface 1482 (shown inFIG. 14B), and acceptor wafer 1497 (first shown in FIG. 14C) may beprepared for wafer bonding as previously described in the incorporatedreferences and low temperature (less than about 400° C.) bonded.

As illustrated in FIG. 14D, bonding oxide layer 1471, back channel layer1405, BOX layer 1403 and remaining channel layer 1407 may be layertransferred to acceptor wafer 1497. Donor wafer bonding oxide layer 1471and acceptor wafer 1497 capping/bonding layer 1431 may be oxide to oxidebonded, thus forming upper isolation layer 1432. The portion of the SOIdonor wafer substrate 1401 that may be above (when the layer stack isflipped over and bonded to the acceptor wafer 1497) the layer transferdemarcation plane 1499 may be removed by cleaving or other lowtemperature processes as described in the incorporated references, suchas, for example, ion-cut with mechanical or thermal cleave or otherlayer transfer methods, thus forming remaining channel layer 1407.

Formation of transistors and devices on the layer being processed 1460without harming the underlying structures of acceptor wafer 1497 mayproceed with a variety of methods. For example, as disclosed in at leastFIGS. 33 and 46 and related specification sections of incorporated byreference U.S. Pat. No. 8,574,929, transistors may be formed with anintegrated heat shields and optical annealing. For example, formation ofCMOS in one transferred layer and the orthogonal connect stripmethodology may be found as illustrated in at least FIGS. 30-33, 73-80,and 94 and related specification sections of U.S. Pat. No. 8,273,610,and may be applied. Low temperature and/or heat shielded 3D stackingtransistor formation techniques may help preserve the effectiveness ofthe trap rich layer by not significantly annealing the defects andtraps.

The exemplary flow herein FIG. 14 is utilizing a similar transistorformation technique as described in incorporated U.S. Patent Application61/889,500 and Ser. No. 14/298,917, by utilizing a TIL, which may beintegrated with TRL 1440/TRL regions 1441, on the top or bottom face, orboth. Or may be one in the same (shown). Many conventional semiconductorprocessing steps may now be utilized to form transistors and devices onthe layer being processed 1460 without harming the underlying structuresof acceptor wafer 1497, for example, a deposition or anneal may beperformed at 800° C. on layer being processed 1460. Heat removal fromthe substrate, for example, such as via a cooled chuck, is described inincorporated U.S. Patent Application 61/889,500.

Processing similar to the processing and transistor/device formationsuch as, for example, illustrated in FIGS. 13D to 13G and described inrelated specification sections herein, or many other semiconductorprocesses and steps, may be performed. For example, as illustrated inFIG. 14E, an exemplary FD-MOSFET structure may be formed. Thestructures, numerals and labels may be common between FIGS. 13A-13G andFIGS. 14A-14E with just the first number adjusted to match the presentfigure.

Formation of CMOS in one transferred layer and the orthogonal connectstrip methodology may be found as illustrated in at least FIGS. 30-33,73-80, and 94 and related specification sections of U.S. Pat. No.8,273,610, and may be applied to at least the FIG. 14 formationtechniques herein. Transferred layer or layers may have regions of STIor other transistor elements within it or on it when transferred, butwould then use alignment and connection schemes for layer transfer ofpatterned layers as described in incorporated patent references.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 14A through 14E are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, a p-channel FD-MOSFET maybe formed with changing the types of dopings appropriately. Moreover,the SOI donor wafer substrate 1401 may be n type or un-doped.Furthermore, transistor and back channel isolation regions 1485 andtransistor isolation region 1487 may be formed by a hard mask definedprocess flow, wherein a hard mask stack, such as, for example, siliconoxide and silicon nitride layers, or silicon oxide and amorphous carbonlayers, may be utilized. Moreover, CMOS FD MOSFETs may be constructedwith n-MOSFETs in a first mono-crystalline silicon layer and p-MOSFETsin a second mono-crystalline layer, which may include differentcrystalline orientations of the mono-crystalline silicon layers, such asfor example, <100>, <111> or <551>, and may include different contactsilicides for optimum contact resistance to p or n type source, drains,and gates. Further, dopant segregation techniques (DST) may be utilizedto efficiently modulate the source and drain Schottky barrier height forboth p and n type junctions formed. Furthermore, raised source and draincontact structures, such as etch and epi SiGe and SiC, may be utilizedfor strain and contact resistance improvements and the damage from theprocesses may be optically annealed. Moreover, a process could be doneon bulk donor wafer rather than an SOI wafer as well to form other typesof transistors without integrated body/back-channel layer/regions.Additionally, the layer transfer process may utilize a method other thanion-cut, for example, a porous layer or selectively etchable layer,detach layer method. Furthermore, a process could be done to form othertypes of transistors on the layer to be processed 1460, for example,FinFets or TFETs. Many other modifications within the scope of theinvention will suggest themselves to such skilled persons after readingthis specification. Thus the invention is to be limited only by theappended claims.

The acceptor wafer herein or in the incorporated references may includea top or near top low-k dielectric layer or layers, as part of the BEOLprocessing and formation. The low-k dielectrics utilized may have alower physical strength, for example as represented by its Young'sModulus, than desired to enable a defect free bond and/or cleave of atransferred layer. Use of a TRL and/or a TIL may also provide a weakerstructure than desired. Preparation for bonding and/or cleaving mayinclude structures and/or materials which include the purpose ofenhancing the physical strength and/or cracking resistance of the stackstructure, especially the bond plane and the acceptor wafer BEOL layers.The top BEOL layer or layers dielectrics may utilize a strongerdielectric material, for example fluorinated oxides or undoped oxides.Furthermore, strengthening regions may be placed within the BEOL, TIL,TRL and/or acceptor wafer to stiffen and/or mechanically strengthen the3DIC structure. Strengthening regions may provide smaller regions of thesofter and weaker low-dielectrics and may mitigate cracking and fractureinitiation and/or propagation. Strengthening regions may includematerials that have a higher Young's modulus than the majority of thematerial within acceptor wafer BEOL, or any TIL or TRL. For example,strengthening regions may include, for example, silicon oxide, which hasa higher mechanical strength than, for example, most low-k dielectrics,such as SiCO, aerogels and silsesquioxanes. Strengthening regions mayinclude less than about 0.5%, less than about 1%, less than about 2%,less than about 5% or less than about 10% of the area and/or volume ofBEOL, or any TIL or TRL. Strengthening regions may include thescribelanes of the wafer, the scribelanes may be processed with stiffermaterial during its formation as part of the process flow, or thematerial within the scribelane may be removed and replaced with astiffer material before layer transfer of a layer above. Moreoverstrengthening regions may be designed to be aligned to the scribelanesand may underlap the full extent of the scribelanes by an underlap,which may be the layout distance between the acceptor die seal and theedge of the closest strengthening regions. For example, the underlap mayhave the dimension of 0 or at least about 1 um, at least about Sum, atleast about 10 um, at least about 20 um, at least about 50 um. A similarstrengthening strategy may be employed on a second layer of device andcircuits when bonding and cleaving a ‘third’ layer on top of the secondlayer. A portion of the strengthening regions may be replaced after thelayer transfer. More teaching on strengthening regions may be found inat least incorporated reference U.S. patent application Ser. No.14/298,917.

Oscillators formed from resonant structures may be integrated as a layerof layers into a 3DIC system or device. The resonant structure mayinclude a silicon based MEMS device and structure, or a piezoelectricformed oscillator, or a hybrid of silicon and piezo material. The MEMSoscillator structure may be integrated in the 3DIC system or device onthe substrate layer, or on a layer/stratum above or below the substratelayer. Other layers or stratum in the 3DIC system stack may provide thecontrol/conditioning circuitry for the MEMS oscillator, for example,circuits such as a PLL, temperature compensation, test and calibrationcircuits, signal conditioning, and/or programmable circuits. The MEMSoscillator may supply at least one clock for a portion or substantiallyall of the 3DIC system or stack device, and may include more than oneMEMS oscillator within a layer/stratum, and may include multiplelayers/stratum of MEMS oscillators. MEMS-based circuits, such asswitches, filters, resonators, oscillators, microphones, loudspeakers,and/or VCOs, for mobile handsets, for example, may be integrated into a3DIC system utilizing techniques described herein and in incorporatedreferences. For example, FIGS. 15A-15G illustrate an integrated MEMSoscillator as a layer within a 3DIC system stack, and an exemplaryprocess flow.

As illustrated in FIG. 15A, a donor wafer substrate 1501 may includeetchstop layer 1505 above buried oxide layer 1503. Etchstop layer 1505may include materials that have substantially zero etchrate or very slowetchrate in an oxide removal etchant, for example, vapor hydrofluoricacid (HF). Etchstop layer 1505 may include, for example, amorphoussilicon, polycrystalline silicon, mono-crystalline (single crystal)silicon, amorphous carbon, silicon nitride. Etchstop layer 1505 mayprovide for an effective etchstop during the eventual resonator bodyrelease step and may have a thickness of, for example, about 25 nm, orabout 20 nm, or about 10 nm, or about 35 nm. Etchstop layer 1505 may bean electrically insulating material (preferred for a simpler processflow) or a conductive one.

As illustrated in FIG. 15B, the top surface of the donor wafer substrate1501 layer stack may be prepared for oxide wafer bonding with adeposition of an oxide or, if of the proper material for oxidation, bythermal oxidation of etchstop layer 1505 to form oxide layer 1571. Alayer transfer demarcation plane (shown as dashed line) 1599 may beformed by hydrogen implantation or other methods as described in theincorporated references, and may reside within the donor wafer substrate1501. The depth of the layer transfer demarcation plane 1599 may be setto provide the desired thickness of the eventual resonator body, whichmay be a thickness of about 20 nm, about 50 nm about 100 nm, about 500nm, about 1000 nm, about 1 um, or about 10 um. The donor wafer substrate1501 stack, such as surface 1582, and acceptor wafer 1510 may beprepared for wafer bonding as previously described and may be lowtemperature (less than approximately 400° C.) bonded. Acceptor wafer1510, as described in the incorporated references, may include, forexample, transistors, circuitry, and metal, such as, for example,aluminum or copper, interconnect wiring, a metal shield/heat sink layeror layers, and thru layer via metal interconnect strips or pads.Acceptor wafer 1510 substrate may be substantially comprised of acrystalline material, for example mono-crystalline silicon or germanium,or may be an engineered substrate/wafer such as, for example, an SOI(Silicon on Insulator) wafer or GeOI (Germanium on Insulator) substrate.Acceptor wafer 1510 may include transistors such as, for example,MOSFETS, FD-MOSFETS, FinFets, FD-RCATs, BJTs, HEMTs, and/or HBTs. Theportion of the donor wafer substrate 1501 that may be above (when thelayer stack is flipped over and bonded to the acceptor wafer 1510) thelayer transfer demarcation plane 1599 may be removed above the layertransfer demarcation plane 1599 by cleaving or other low temperatureprocesses as described in the incorporated references, such as, forexample, ion-cut with mechanical or thermal cleave or other layertransfer methods, thus forming remaining resonator layer 1507.

As illustrated in FIG. 15C, oxide layer 1571, etchstop layer 1505,buried oxide layer 1503 and remaining resonator layer 1507 may be layertransferred to acceptor wafer 1510. Oxide layer 1571 and any bondingoxides on acceptor wafer 1510 are now illustrated as bottom oxide layer1580. The top surface of remaining resonator layer 1507 may bechemically or mechanically polished, and/or may be thinned by lowtemperature oxidation and strip processes, such as the TEL SPA toolradical oxidation and HF:H₂O solutions as described in referencedpatents and patent applications. Thru the processing, the wafer sizedlayer remaining resonator layer 1507 could be thinned from its originaltotal thickness, and its final total thickness could be in the range ofabout 15 nm to about 10 um. Acceptor wafer 1510 may include one or more(two are shown in this example) shield/heat sink layers 1588, which mayinclude materials such as, for example, Aluminum, Tungsten (a refractorymetal), copper, silicon or cobalt based silicides, or forms of carbonsuch as carbon nanotubes, and may be layered itself, for example, asdescribed herein FIG. 3. Each shield/heat sink layer 1588 may have athickness range of about 150 nm to about 1 mm, for example, about 150nm, about 100 nm, about 200 nm, about 300 nm, about 1500 nm, about 0.1um, about 1 um, about 2 um, and about 10 um. Shield/heat sink layer 1588may include isolation openings 1587, and alignment mark openings (notshown), which may be utilized for short wavelength alignment of toplayer (donor) processing to the acceptor wafer alignment marks (notshown). Shield/heat sink layer 1588 may include one or more shield pathconnects 1585 and shield path vias 1583. Shield path via 1583 maythermally and/or electrically couple and connect shield path connect1585 to acceptor wafer 1510 interconnect metallization layers such as,for example, exemplary acceptor metal interconnect 1581 (shown). Shieldpath connect 1585 may also thermally and/or electrically couple andconnect each shield/heat sink layer 1588 to the other and to acceptorwafer 1510 interconnect metallization layers such as, for example,acceptor metal interconnect 1581, thereby creating a heat conductionpath from the shield/heat sink layer 1588 to the acceptor substrate1595, and a heat sink (not shown). Isolation openings 1587 may includedielectric materials, similar to those of BEOL isolation 1596. Acceptorwafer 1510 may include first (acceptor) layer metal interconnect 1591,acceptor wafer transistors and devices 1593, and acceptor substrate1595. Various topside defect anneals may be utilized at this step orlater in the process flow, for example, during the resonator bodyevacuation and seal step. For example, an optical beam such as the laserannealing previously described may be utilized, as described elsewhereherein and in incorporated references. Heat generated by the opticalanneal may be absorbed by shield/heat sink layer 1588 regions anddissipated internally and/or laterally and may keep the temperature ofunderlying metal layers, such as metal interconnect 1581, and othermetal layers and BEOL dielectrics below it, cooler and prevent damage.Shield/heat sink layer 1588 and associated dielectrics may laterallyspread and conduct the heat generated by the topside defect anneal, andin conjunction with the dielectric materials (low heat conductivity)above and below shield/heat sink layer 1588, keep the interconnectmetals and low-k dielectrics of the acceptor wafer interconnect layerscooler than a damage temperature, such as, for example, about 400° C. Asecond layer of shield/heat sink layer 1588 may be constructed (shown)with a low heat conductive material sandwiched between the two heat sinklayers, such as silicon oxide or carbon doped ‘low-k’ silicon oxides,for improved thermal protection of the acceptor wafer interconnectlayers, metal and dielectrics. Shield/heat sink layer 1588 may act as aheat spreader. Electrically conductive materials may be used for the twolayers of shield/heat sink layer 1588 and thus may provide, for example,a Vss and a Vdd plane and/or grid that may be connected to the donorlayer transistors above, as well may be connected to the acceptor wafertransistors below, and/or may provide below transferred layer deviceinterconnection. Noise on the power grids, such as the Vss and Vdd planepower conducting lines/wires, may be mitigated by attaching/connectingdecoupling capacitors onto the power conducting lines of the grids. Thedecoupling caps, which may be within the second layer (donor, forexample, donor wafer device structures) or first layer (acceptor, forexample acceptor wafer transistors and devices 1593), may include, forexample, trench capacitors such as described by Pei, C., et al., “Anovel, low-cost deep trench decoupling capacitor for high-performance,low-power bulk CMOS applications,” ICSICT (9^(th) InternationalConference on Solid-State and Integrated-Circuit Technology) 2008,October 2008, pp. 1146-1149, of IBM. The decoupling capacitors mayinclude, for example, planar capacitors, such as poly to substrate orpoly to poly, or MiM capacitors (Metal-Insulator-Metal). Shield/heatsink layer 1588 may include materials with a high thermal conductivitygreater than 10 W/m-K, for example, copper (about 400 W/m-K), aluminum(about 237 W/m-K), Tungsten (about 173 W/m-K), Plasma Enhanced ChemicalVapor Deposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), andChemical Vapor Deposited (CVD) graphene (about 15000 W/m-K). Shield/heatsink layer 1588 may be sandwiched and/or substantially enclosed bymaterials with a low thermal conductivity (less than about 10 W/m-K),for example, silicon dioxide (about 1.4 W/m-K). The sandwiching of highand low thermal conductivity materials in layers, such as shield/heatsink layer 1588 and under & overlying dielectric layers, may spreadand/or absorb the localized heat/light energy of the topside anneallaterally and protects the underlying layers of interconnectmetallization & dielectrics, such as in the acceptor wafer 1510, fromharmful temperatures or damage. When there may be more than oneshield/heat sink layer 1588 in the device, the heat conducting layerclosest to the second crystalline layer or bottom oxide layer 1580 maybe constructed with a different material, for example a high meltingpoint material, for example a refractory metal such as tungsten, thanthe other heat conducting layer or layers, which may be constructedwith, for example, a lower melting point material, for example such asaluminum or copper. Now transistors may be formed with low effectivetemperature (less than approximately 400° C. exposure to the acceptorwafer 1510 sensitive layers, such as interconnect and device layers)processing, and may be aligned, for example to a less than about 40 mmalignment tolerance, to the acceptor wafer alignment marks (not shown)as described in the incorporated references. This may include furtheroptical defect annealing or dopant activation steps. The remaining donorwafer substrate 1501 may now be processed, such as smoothing andannealing, and reused for additional layer transfers.

Alternatively, etchstop layer 1505 may be deposited directly ontoacceptor wafer 1510 (bottom oxide layer 1580 may or may not benecessary), and then remaining resonator layer 1507 may be transferredto acceptor wafer 1510 with etchstop layer 1505 (and any bonding oxideif wafer bonding is utilized) thus forming the structure in FIG. 15C.

As illustrated in FIG. 15D, portions of remaining resonator layer 1507may be removed from various regions utilizing photolithography and etchtechniques, which may include a hard mask, thus forming resonator body1520, resonator drive/sense electrodes 1522 and dummy regions 1523. Theetching of remaining resonator layer 1507 may include overetching into aportion of buried oxide layer 1503, to ensure a full release ofresonator body 1520 at a later step. Optionally, a deeper etch in onlythe regions where a stratum to stratum connection is to eventually bemade, for example, between dummy region 1523 and resonator body 1520 inthe illustration, may be performed, wherein the etch may extendsubstantially thru the etchstop layer 1505. This optional mask and etchmay be done before or after the mask and etch of the resonator body1520, and may lower the TLV to TLV leakage depending on the conductivityof the material used for etchstop layer 1505 and may provide preparationfor a liner-less vertical conductive connection.

As illustrated in FIG. 15E, an oxide may be deposited and patterned tocover selected parts of the resonator while providing openings forelectrical contact to the drive/sense electrodes 1522. Thus, resonatoroxide regions 1526 may be formed. Resonator etchcap 1528 may bedeposited, which may be preceded by a surface clean to provide goodconnection to the open topside contact regions of the drive/senseelectrodes 1522. Resonator etchcap 1528 may include a material that issubstantially impervious to the eventual oxide etch resonator releasechemistry, for example, amorphous silicon or poly silicon layer may bedeposited, and may provide electrical contact/connection to thedrive/sense electrodes 1522. Vent openings 1529 may then be formed toaccess the resonator oxide regions 1526, and may include a mask and etchof regions of resonator etchcap 1528.

Resonator body 1520 may include complex shapes, for example, combs, beamwebs, discs, and may be surrounded by driving and sensing electrodes,such as drive/sense electrodes 1522, with transducer gaps. Generally thebulk of the resonator body motion may be induced by electrostaticdynamics. A hybrid resonator body may include a piezoelectric materialdeposited onto the silicon resonator body, for example, AlN or ZnO, andthe hybrid resonator body motion may be induced by piezoelectricexcitation.

As illustrated in FIG. 15F, portions of resonator oxide regions 1526 andoxide layer 1503 may be removed to release resonator body 1520. Theremoval may utilize a vapor phase etchant, for example, vaporhydrofluoric acid (HF), to remove substantially all the oxidesurrounding resonator body 1520, thus forming resonator chamber 1521. Aplasma based etch process may be utilized, especially as the gaps anddimensions become very small and surface effects dominate. Thus, upperoxide regions 1526, upper interior oxide regions 1536, and lower oxideregions 1533 may be formed and remain, providing strength and electricalisolation to various structures within the resonator layer. Theresonator body 1520 may now be cleaned and then contemporaneously sealedin a vacuum to minimize water and other contaminates on or close toresonator body 1520 which may cause frequency drift due to mass loadingof resonator body 1520. Depending on the thermal isolation strategyutilized in forming the 3DIC system stack, various methods of cleaningmay be utilized. As illustrated herein FIG. 15 with a shield, an opticalheating of the resonator layer silicon in the presence of gases such asHCl or H₂+Cl₂, and/or O₂, may clean up residues on resonator body 1520and in resonator chamber 1521. The spaces may be evacuated to about 10mT and the vent openings 1529 may be sealed whilst under vacuum withseal layer 1540. Seal layer 1540 may include, for example,polycrystalline silicon, amorphous silicon.

As illustrated in FIG. 15G, seal layer 1540 may be CMP′d flat and trenchisolation regions 1560 may be formed by conventional 3DIC stack(effective low temperature exposure of underlying BEOL materials) etchand fill techniques. TLVs 1570 and resonator layer interconnectmetallization 1572 may be formed to electrically and/or thermallyconnect the resonator layer/stratum with the underlying (or overlying ifrequired) acceptor substrate 1510 interconnect, transistors andcircuits, as well as providing heat conduction paths to heat sinks asdescribed herein and incorporated references.

Alternatively or in addition, one or more MEMS oscillators may be formedon the substrate, such as acceptor wafer 1510, and then CMOS transistorsand circuits may be formed on top utilizing many of the stacking and3DIC device formation techniques herein and incorporated references.

Temperature limitations may be imposed on processing steps aboveacceptor wafer 1510 depending on the mitigation techniques utilized,such as TIL, TES, etc. Even shield/heat sink layers 1588 may not benecessary depending on the topside optical heat treatment chosen as partof the detailed process flow design choices.

The MEMS oscillator taught in at least FIG. 15 herein may be combinedwith an RF coil having an air- or vacuum-isolated character, which isafforded by the same processing which leads to the MEMS oscillator.

References related to MEMS devices, particularly encapsulatedoscillators (for use in clocks), accelerometers, and pressure sensorsmay include Partridge, Aaron, Markus Lutz, Bongsang Kim, MatthewHoperoft, Rob N. Candler, Thomas W. Kenny, Kurt Petersen, and MasayoshiEsashi. “MEMS resonators: getting the packaging right.” Semicon Japan(2005); Candler, Rob N., Matthew A. Hoperoft, Bongsang Kim, Woo-TaePark, Renata Melamud, Manu Agarwal, Gary Yama, Aaron Partridge, MarkusLutz, and Thomas W. Kenny. “Long-term and accelerated life testing of anovel single-wafer vacuum encapsulation for MEMS resonators.”Microelectromechanical Systems, Journal of 15, no. 6 (2006): 1446-1456;and Flannery, Anthony Francis, and Steven S. Nasiri. “Verticallyintegrated MEMS structure with electronics in a hermetically sealedcavity.” U.S. Pat. No. 7,104,129, issued Sep. 12, 2006; the contents ofthe foregoing incorporated by reference.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 15A through 15G are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, barrier metals may bechosen to facilitate good electrical contact between resonator layerinterconnect metallization 1572 and drive/sense electrodes 1522.Moreover, trench isolation regions 1560 formation may include the areasfor resonator drive/sense electrode connections, etching out seal layer1540 and may etch out resonator etchcap 1528, to provide an improvedconnection to drive/sense electrodes 1522. Furthermore, additional layeror layers of transistors and other devices may be formed on top of theresonator layer as part of the 3DIC system stack. Moreover, etchstoplayer 1505 may be formed thicker than about 35 nm and may affect thedensity of vertical interconnects and TLV to TLV leakage. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus theinvention is to be limited only by the appended claims.

FIGS. 16A to 16K describe an exemplary process flow utilizing a carrierwafer or a holder wafer or substrate wherein CMOS transistors may beprocessed on two sides of a donor wafer. PMOS and NMOS transistors maybe formed on each of the two sides or NMOS on one side and PMOS on theother, and then the two sided structure (NMOS on top of PMOS or CMOS ontop of CMOS, or a combination thereof) donor wafer may be transferred toan target or acceptor substrate with pre-processed circuitry. State ofthe art CMOS transistors and compact 3D library cells may be constructedwith methods that may be suitable for 3D IC manufacturing. The exemplaryprocess flow of FIGS. 16A to 16J describe NMOS on one side and PMOS onthe other for simplicity, however, CMOS on one side or both sides of thedonor wafer may employ the techniques in referenced and incorporateddocuments; for example, in at least FIGS. 70-80 and associatedspecification of U.S. Pat. No. 8,273,610.

As illustrated in FIG. 16A, a Silicon On Oxide (SOI) donor wafersubstrate 1600 may be processed in the typical state of the art HKMGgate-last manner up to the step prior to where CMP exposure of thepoly-crystalline silicon dummy gates takes place, but forming only NMOStransistors (in this exemplary case). SOI donor wafer substrate 1600,the buried oxide (i.e., BOX) 1601, the thin silicon layer 1602 of theSOI wafer, the shallow trench isolation (STI) 1603 among NMOStransistors, the ‘dummy’ poly-crystalline silicon 1604 and gatedielectric 1605 of the NMOS dummy gates, NMOS source and drains 1606,NMOS transistor channel 1607, and NMOS interlayer dielectric (ILD) 1608are shown in the cross-section illustration. These structures of FIG.16A illustrate the substantial completion of the first phase of NMOStransistor formation. The thermal cycles of the NMOS HKMG process up tothis point in the flow may be adjusted to compensate for later thermalprocessing.

As illustrated in FIG. 16B, a layer transfer demarcation plane (shown asdashed line) 1699 may be formed in SOI donor wafer substrate 1600 byhydrogen implantation 1610 or other methods as previously described inat least the incorporated documents.

As illustrated in FIG. 16C, oxide 1616 may be deposited onto carrier orholder wafer 1620 and then both the SOI donor wafer substrate 1600 andcarrier or holder wafer 1620 may be prepared for wafer bonding aspreviously described, and then may be oxide to oxide bonded together atinterface 1614. Carrier or holder wafer 1620 may also be called acarrier or holder substrate, and may be composed of mono-crystallinesilicon, or other materials.

As illustrated in FIG. 16D, the portion of the SOI donor wafer substrate1600 that may be below the layer transfer demarcation plane 1699 may beremoved by cleaving or other processes as previously described in atleast the incorporated documents, such as, for example, ion-cut or othermethods. The remaining donor wafer layer 1600′ may be thinned bychemical mechanical polishing (CMP) and surface 1622 may be prepared fortransistor formation. Damages from the ion-cut processing may berepaired by at least methods disclosed herein and in the incorporateddocuments; for example, short wavelength laser annealing.

As illustrated in FIG. 16E, donor wafer layer 1600′ at surface 1622 maybe processed in the typical state of the art HKMG gate last processingmanner up to the step prior to where CMP exposure of thepoly-crystalline silicon dummy gates takes place to form the PMOStransistors with dummy gates. The PMOS transistors may be preciselyaligned at state of the art tolerances to the NMOS transistors as aresult of the shared substrate possessing the same alignment marks.Carrier or holder wafer 1620, oxide 1616, BOX 1601, the thin siliconlayer 1602 of the SOI wafer, the shallow trench isolation (STI) 1603among NMOS transistors, the poly-crystalline silicon 1604 and gatedielectric 1605 of the NMOS dummy gates, NMOS source and drains 1606,the NMOS transistor channels 1607, and the NMOS interlayer dielectric(ILD) 1608, donor wafer layer 1600′, the shallow trench isolation (STI)1633 among PMOS transistors, the poly-crystalline silicon 1634 and gatedielectric 1635 of the PMOS dummy gates, PMOS source and drains 1636,the PMOS transistor channels 1637, and the PMOS interlayer dielectric(ILD) 1638 are shown in the cross section illustration. A hightemperature anneal may be performed to activate both the NMOS and thePMOS transistor dopants. These structures of FIG. 16E illustratesubstantial completion of the first phase of PMOS transistor formation.The PMOS transistors may now be ready for typical state of the artgate-last transistor formation completion.

As illustrated in FIG. 16F, the PMOS ILD 1638 may be chemicalmechanically polished to expose the top of the PMOS poly-crystallinesilicon dummy gates, composed of poly-crystalline silicon 1634 and gatedielectric 1635, and the dummy gates may then be removed by etching. Ahi-k gate dielectric 1640 and the PMOS specific work function metal gate1641 may be deposited. An aluminum fill 1642 may be performed and themetal chemical mechanically polished. A low temperature dielectric layer1639 may be deposited and the typical gate 1643 and source/drain 1644contact formation and metallization may now be performed to connect toand among the PMOS transistors. Partially formed PMOS inter layer via(ILV) 1647 may be lithographically defined, plasma/RIE etched, andmetallization formed. Oxide layer 1648 may be deposited to prepare forbonding. Furthermore, the gate dielectric on transistors may havedifferent dielectric permittivities than silicon dioxde. The gatedielectric permittivity of the second layer transistors may be differentthan the gate dielectric permittivity of the first layer transistors.

As illustrated in FIG. 16G, a damage plane or layer (shown as dashedline) 1698 may be formed in carrier or holder wafer 1620 by opticalmeans 1671, for example a two-phonon exposure with lasers, wherein thedepth of the two-phonon interaction may be controlled with optics.Silicon to silicon bonds may be broken in a 2-phonon interaction,forming a layer or plane of silicon vacancies and silicon interstitialatoms (sometimes called interstitial vacancy pairs). Optical means 1671may be employed thru carrier or holder wafer 1620 to minimize 1-phononinteractions with doped regions and metal layers, or may be employedthru the processed layers (from ‘below in the FIG. 16G context, notshown), or a combination of both.

As illustrated in FIG. 16H, the donor wafer surface at oxide layer 1648and top oxide surface of acceptor or target substrate 1688 with acceptorwafer metal connect strip 1650 may be prepared for wafer bonding aspreviously described and then low temperature (less than approximately300° C.) aligned and oxide to oxide bonded at interface 1651. Theprocess temperature is preferred as low as possible to mitigatereconstitution of the interstitial vacancy pairs of damage plane orlayer 1698. The acceptor metal strip and donor metal strip methodology,described in at least FIGS. 71, 72-80 and associated specification ofincorporated U.S. Pat. No. 8,273,610, and may employ a machine such asthe EV Group Gemini FB XT, which may provide alignment of thicksubstrates to within 200 nm. Small acceptor squares of maximummisalignment dimensions, may also be utilized, to connect the donorwafer metal TLV to the acceptor wafer metallization, such as describedin at least FIG. 75 of the above patent.

As illustrated in FIG. 16I, the portion of the carrier or holder wafer1620 that may be above damage plane or layer 1698 may be removed bycontrolled stress methods. A polymer or co-polymer layer 1673 may bedeposited on canier or holder wafer 1620 (shown in FIG. 16H forclarity). Polymer or co-polymer layer 1673 may also be deposited on thebackside acceptor or target substrate 1688 (not shown). Thethickness(es) of polymer or co-polymer layer 1673 on either side of theentire structure may be tuned to provide the proper stress levels tocleave at damage plane or layer 1698 when exposed to a thermal stress.Polymer or co-polymer layer 1673 may incorporate a release layer tofacilitate an easy release from whichever surface it was applied to. Athermal stress, for example, immersion or spray of LN2 (Liquid Nitrogen)may be used as a stress for cleaving. Details and demonstration of thepolymer stress and optical vacancy creation cleaving methods for siliconwafering of an ingot may be found with Siltectra GmbH atwww.siltectra.com and patent disclosures of Lukas Lichtensteiger, suchas US Patent Application Publication 2011/0259936 and internationalpublication WO2014005726. These stress techniques may be applied toother process flows within the incorporated references; for example, atleast FIGS. 81 and 82 and associated specification of U.S. Pat. No.8,273,610. The remaining layer of the canier or holder wafer 1620remaining on the structure attached to oxide layer 1616 may be removedby chemical mechanical polishing (CMP) to or into oxide layer 1616. Withconventional sidewall and backside protection, chemical means may alsobe employed, for example, warm KOH, to remove remaining layer of thecanier or holder wafer 1620. The remaining bulk of canier or holderwafer 1620 may be recycle or reclaimed for additional uses, such asreuse as a carrier wafer. The NMOS transistors may be now ready fortypical state of the art gate-last transistor formation completion.

As illustrated in FIG. 16J, oxide 1616 and the NMOS ILD 1608 may bechemical mechanically polished to expose the top of the NMOS dummy gatescomposed of poly-crystalline silicon 1604 and gate dielectric 1605, andthe dummy gates may then be removed by etching. A hi-k gate dielectric1660 and an NMOS specific work function metal gate 1661 may bedeposited. An aluminum fill 1662 may be performed and the metal chemicalmechanically polished. A low temperature dielectric layer 1669 may bedeposited and the typical gate 1663 and source/drain 1664 contactformation and metallization may now be performed to connect to and amongthe NMOS transistors. Partially formed NMOS inter layer via (ILV) 1667may be lithographically defined, plasma/RIE etched, and metallizationformed, thus electrically connecting NMOS ILV 1667 to PMOS ILV 1647.

As illustrated in FIG. 16K, oxide 1670 may be deposited and planarized.Thru layer via (TLV) 1672 may be lithographically defined, plasma/RIEetched, and metallization formed. TLV 1672 electrically couples the NMOStransistor layer metallization to the acceptor or target substrate 1688at acceptor wafer metal connect strip 1650. A topmost metal layer, at orabove oxide 1670, of the layer stack illustrated may be formed to act asthe acceptor wafer metal connect strips for a repeat of the aboveprocess flow to stack another preprocessed thin mono-crystalline siliconlayer of NMOS on top of PMOS transistors.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 16A through 16K are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistor layers oneach side of BOX 1601 may include full CMOS, or one side may be CMOS andthe other n-type MOSFET transistors, or other combinations and types ofsemiconductor devices. Additionally, the above process flow may also beutilized to construct gates of other types, such as, for example, dopedpoly-crystalline silicon on thermal oxide, doped poly-crystallinesilicon on oxynitride, or other metal gate configurations, as ‘dummygates,’ perform a layer transfer of the thin mono-crystalline layer,replace the gate electrode and gate oxide, and then proceed with lowtemperature interconnect processing. Moreover, that other transistortypes may be possible, such as, for example, RCAT, FinFet, andjunction-less. Further, the donor wafer layer 1600′ in FIG. 16D may beformed from a bulk mono-crystalline silicon wafer with CMP to the NMOSjunctions and oxide deposition in place of the SOI wafer discussed.Additionally, the SOI donor wafer substrate 1600 may start as a bulksilicon wafer and utilize an oxygen implantation and thermal anneal toform a buried oxide layer, such as, for example, the SIMOX process(i.e., separation by implantation of oxygen), or SOI donor wafersubstrate 1600 may be a Germanium on Insulator (GeOI) wafer. The layertransfer of FIG. 16F-161 may be effected by forming a layer demarcationplane in carrier or holder wafer 1620 by hydrogen implantation. Stresslayers, embedded & raised source/drains, and other conventional HKMGrelated techniques may be utilized in the exemplary process flow withinthe temperature constraints of each step. Many other modificationswithin the scope of the invention will suggest themselves to suchskilled persons after reading this specification. Thus the scope of theinvention is to be limited only by the appended claims.

An embodiment of the invention may include various modification of theprocess flows described in U.S. Pat. No. 8,273,610 in relation to atleast FIGS.: 70A-70F, 81A-81F, 82A-82G, 83A-83L. These flows may startwith a donor wafer which may go through a normal process flow to form acircuit layer which we could call stratum-3. The described flow suggeststhe use of a ‘gate-replacement’ flow, also called ‘gate-last’ flow fortransistor formation, although other structures/techniques may beutilized. The stratum-3 layer would be first transferred, for example,using ion-cut, to a carrier wafer/substrate and then transferred on topof a target wafer (also called base or acceptor wafer/substrate in somecircumstances). Once on top of the target wafer the dummy oxide and thedummy gate could be replaced with the gate last gate stack of, forexample, hafnium oxide and metal gate. This flow provides the advantagethat any damage caused by the ion-cut would be removed by thereplacement step. In an embodiment the replacement oxide and gate couldbe made with silicon oxide and poly gate which are in most cases cheaperand easier to process. So the repair of the ion-cut potential damage isnot a condition of having high-K metal gate process. It should be notedthat once stratum-3 is bonded on the target wafer the temperaturelimitation, generally restricted to less than 400° C., due to theunderlying structure does exist. Therefore, a process should be used forthe deposition of a high quality gate oxide at the metallizationcompatible temperatures. Furthermore, the dummy gate stack may bereplaced after the ion-cut by other types of gate stacks; for example,such as a grown or deposited oxide/dielectric with apolysilicon/polycide electrode, or a grown or deposited oxide/dielectricwith a tungsten electrode. Such processes have been presented in atleast U.S. Pat. No. 8,273,610.

While ion-cut is a good option for cutting a less than a micron thicklayer from the donor wafer transferring it to the carrier wafer, otherlayer transfer options do exist. It also should be noted that thetransferred layer could had been fully processed first to includetransistors and isolation, or alternatively the transferred layer mightbe just a mono-crystal layer, giving up stratum-3 in the layer transfer.

In the following we outline few alternative process flows to ion-cutavailable for transferring a layer from a donor wafer to either acarrier wafer or to the final target wafer:

A. Use of donor wafer that has been pre-processed for a future cut/layertransfer such as:

1) Pre-cut by laser, as described in at least US patent application US2014/0038392—this patent publication is hereby incorporated by referencein this application;

2) Use an SOI wafer or construct an SOI wafer;

3) Use an ELTRAN treated wafer with a porous layer before the top highquality layer, or construct an ELTRAN wafer;

4) Use a wafer with etch stop indicators pre-defined (LTDP-LayerTransfer Demarcation Plugs) as is been described in relation to FIG. 150of incorporated U.S. Pat. No. 8,273,610.

B. Use a laser, as described in US patent application 2014/0038392, tocut the desired transfer layer off the donor wafer after high (over 400°C.) processes for stratum-3 are completed.

C. Use ‘Cold Split’ technology, for example, as developed and offered bycommercial company called Siltectra (http://www.siltectra.com) and beendescribed in at least US Patent Applications 2011/0259936—this patentpublication is hereby incorporated by reference in this application.

Some of the above techniques are better used for a thicker layer of fewmicrons, generally due to the variability of depth of the ‘cut’ of thetransfer process. So after the transfer layer has been bonded to thecarrier wafer or the target wafer and cut off the donor wafer, anadditional process or processes could be used to thin the transferredlayer further to about one of the following device thickness targets:about 20 nm, or about 50 nm, or about 100 nm, or about 200 nm or about400 nm. Alternatives for such additional processing could include thefollowing:

A. Etch, grind and Chemical Mechanical Polishing (CMP), which mightinclude some sensing of depth control;

B. Etch, grind and Chemical Mechanical Polishing-CMP, which mightinclude an stop indicator scheme, for example, such as described abovewith respect to LTDP;

C. Forming an etch stop or other types of a detach layer and thenprocessing an epitaxial layer on which the donor transistors areconstructed. For example, an ion implantation and anneal may be utilizedto form an etch stop layer, either on the donor surface or buried, andthen a device epitaxial layer may be formed on top. A diffusion processmay be utilized to form a doped etch-stop layer, and then a deviceepitaxial layer may be formed on top. An etch-stop layer may include,for example, heavily doped p+ or doped n+ silicon, depending on thechemistries used for selectivity of the etch-stop etching. Etch stoplayer may include a material such as SiGe. Furthermore, a singleepitaxial process may start with a light doping, then switch to a heavydoping (or change type) and then back to a light or undoped epitaxialdeposition, thus forming two or more layers of differing dopantconcentration and/or type. An ‘etch-stop’ may mean a significant(usually greater than a 5-10× etch rate) slowing of the etch removalrate so that control of the endpoint layer and planarity with respect tothe desired device surface may be achieved. Many etch stop techniquesfor layer transfer may be described in at least FIGS. 14, 139-140, and230-232 of incorporated U.S. Pat. No. 8,273,610.C. Use of a secondary ion-cut of the bonded layer to trim thetransferred layer down to a precisely controlled thickness and thicknessvariation across the wafer/substrate. This does avoid the ion damagefrom the thin layer as the ion implant is done from the back of thetransfer layer. Following the ion cut some etch or CMP should be used tofurther treat the surface.

In addition some anneal might also be used to further treat thetransferred layer for future step.

It should be noted that in most of these alternatives the donor wafercould be treated after the layer transfer to repair the top layersurface and prepare the donor wafer for additional steps of layertransfer.

The secondary ion-cut could be tuned to overcome some limitation of thefirst cut techniques such as un-even thickness of the transferred layer.A measurement tool could be used to create a depth profile of the wafersurface. The depth profile could be then transfer to an ion implantertool which will adjust the ion (H+) implant depth accordingly. Thus aprecise and well controlled ion-cut damage layer, or layer transferdemarcation layer, may be formed in the transferred layer.

This combination of cut techniques could allow for high quality thin (20nm-200 nm) layer transfer. This could be done to a layer that has gonethrough process of complete or partial front end process of stratum-3without damaging the sensitive transistor formation of stratum-3.

To assist the layer depth measurement, the bonding layers could bespecially engineered to enhance the accuracy of such depth profilemeasurement. An example for such could be layering silicon oxide andsilicon nitride to form a reflective layer tuned to reflect a laserwavelength of the measurement tool. Or including a metal layer if thereflective layer is on the target wafer. In U.S. Pat. No. 4,827,325,incorporated here by reference, such reflective layering is presented.

The donor wafer/substrate with a detach and/or etchstop layer orstructure may be processed in the manufacturing flow and facility of thedevice stack manufacturer, or may be constructed at a wafer supplier andbought by the wafer stack manufacturer as a ‘pre-made’ substrate. Afteruse in the stack formation flow, the wafer stack manufacturer mayperform reclaim or recycle processing on the used donor wafer/substrateor may deliver it back to the wafer supplier for reclaim and/orrecycle—reprocessing may include a fresh detach and/or etchstop layer orstructure in the donor wafer/substrate. For example, a wafer supplier,such as, for example, SunEdison, may process a prime silicon wafer witha porous detach layer covered on one side by an epitaxial layer ofsilicon made to order (thickness, doping, etc.) for the specific waferstack flow and device desired by the wafer stack manufacturer. Thusforming a Si-dDS, a silicon topped detachable donor substrate. The waferstack manufacturer, for example Intel or Samsung, utilizes the Si-dDS ina stack process flow with a detach step, and then returns the usedSi-dDS to SunEdison for recycle or reclaim.

In U.S. Pat. No. 8,273,610, FIG. 81 (A to F) transferring a full processstratum-3 is described—7032, 7028, 7026, 7030, 7008, from a donor wafer8100 to a target wafer 808.

In FIG. 82 of U.S. Pat. No. 8,273,610 transferring the stratum-3layer—8202 off a donor wafer 8206A, first to a carrier wafer 8226 andthen from the donor wafer using a second ion-cut 8218 to the targetwafer 808, is described.

In U.S. Pat. No. 8,273,610, FIG. 83 (A to K) the transfer of a stratum-3layer—8302+ from a donor wafer 8300A first to a carrier wafer 8320, thenprocess stratum-2-8300+ on the other side of the transferred layer whileit is on the carrier wafer 8320 is described.

And then from the carrier wafer the layer comprising stratum-2 andstratum-3 (as dual strata 400) is transferred on to the target wafer 808using a second ion cut 8321.

The ion-cut may be associated with defects caused by the ion implantprocess. The defects may be repaired with high temperature processing,such as previously described at least herein and in incorporatedreferences, for example, thermal treatments such as RTA, RTO, furnaceannealing, laser annealing. Ion-cut damage to sensitive areas may beavoided by backside ion-cut, by screening the H+(and any co-implant)from the sensitive device areas (gate, source rain junctions, etc.) suchas described in at least FIG. 70B-1 of incorporated U.S. Pat. No.8,273,610. The gate stack may be replaced after the ion-cut ion-implant,such as described herein and in incorporated references. For example,the dummy gate stack may be replaced by HKMG stack or by an oxidedielectric and poly/polycide gate electrode. The ion-cut ion implant mayalso be performed prior to the gate formation if the subsequent thermalcycles allow such, to avoid premature cleave/release.

Furthermore, alternative cut techniques presented before in respect forthe transfer layer from the donor wafer could be used here as well.

Yet the transfer from the carrier wafer opens up more options since:

A. The carrier wafer is not the one contributing the device layer andtherefore does not have to have a top layer of high quality to supporttransistor formation accordingly:

1) The carrier wafer may be built from low cost test wafers, which couldbe ground and/or etched away, or other alternatives in some flows(depending on for example thermal and/or sheer stresses of post attachprocessing), for example, glass substrates;

2) The carrier wafer may have a top layer which is designed for detachsuch as:

-   -   a) Porous layer (variation of the ELTRAN technique), which may        be buried by, for example, epitaxial silicon and oxide, thereby        providing an ox-ox bond from carrier to transfer layer, and may        include release ports in the transfer layer scribelanes and/or        interior to each die;    -   b) Other porous structures such as Aerogel materials, and may        include release ports in the transfer layer scribelanes and/or        interior to each die (may include aerogels and techniques        described in U.S. patent application Ser. No. 14/298,917,        incorporated by reference;    -   c) Photo-resist;

3) The carrier wafer could be designed for layer release as described inU.S. Pat. No. 8,273,610 in relation to at least FIG. 184, and/or toFIGS. 185, 186, 187, 188, 189.

4) The carrier wafer may include a top layer which is designed fordetach such as a buried layer of laser damaged silicon, for example,such as described in at least FIG. 5A of U.S. Patent Publication No.2014/0038392 to Yonehera, et al., of Solexel Corporation.

Note: The carrier wafer could be covered with oxide to support goodbonding to the transfer layer. Other bonding layers could also be used.

B. There is a natural barrier between the carrier wafer and thetransferred layer carrying stratum-2 and stratum-3 (dual strata 400)—thebonding layer. The bonding layer could be an oxide and would provide anetch stop. Accordingly the whole carrier wafer could be ground or etchedaway to that oxide layer after the bonding to the target wafer.Alternatively if any of the other techniques is used to cut thetransferred layer from the carrier wafer and if such might leave someportion still attached, then it could be easily etched away. Forexample, forming a thin buried etch-stop layer within the carrier wafer,either buried or at the surface (and then coat with oxide for an ox-oxbond) may be utilized. In most cases this will be cheaper than the useof a secondary ion-cut as presented before in respect to the flow withthe donor wafer.

The release from the carrier wafer may depend on the choice of processand may include any of steps such as: anneal step, mechanical pulling orforce application from top and/or mechanical side stress, water jet toform side stress, laser side stress, knife edge side stress, etching orcooling step (thermal shock or thermal exposure), perforated carrier andselective etchant release as described and referenced herein. Therelease procedure may include providing release ports in the transferlayer scribelanes and/or interior to each die. The release procedure mayutilize a frontside release, may include providing frontside releaseports in the transfer layer scribelanes and/or interior to each die.Release utilizing an oxide layer may include a wet HF, vapor-phase HF, aMEMS style Bosch DRIE etch (alternating SF₆ and C₄F₄ plasma etches).Silicon release etches on the porous silicon may include KOH, XeF₂and/or EDP or TMAH. Substances such as supersaturated CO₂ may help witha stiction free release as well as precise design and spacing of therelease etchant ports.

Furthermore, the carrier wafer/substrate may include etch stopindicators pre-defined (LTDP-Layer Transfer Demarcation Plugs) as isbeen described in relation to FIG. 150 of incorporated U.S. Pat. No.8,273,610. This may be used in combination with other releasetechniques; for example, the Siltectra stress or Solexel laser damagelayer. The LTDPs may assist a ‘rough’ cleave technique (such as theSolexel stress cleave) to have an endpoint that may form a preciselydefined, flat and parallel to the device surface cleave or allow acleanup CMP/etch after a ‘rough’ cleave to have the same.

The carrier wafer/substrate with a detach and/or etchstop layer orstructure may be processed in the manufacturing flow and facility of thedevice stack manufacturer, or may be constructed at a wafer supplier andbought by the wafer stack manufacturer as a ‘pre-made’ substrate. Afteruse in the stack formation flow, the wafer stack manufacturer mayperform reclaim or recycle processing on the used carrierwafer/substrate or may deliver it back to the wafer supplier for reclaimand/or recycle—reprocessing may include a fresh detach and/or etchstoplayer or structure in the carrier wafer/substrate. For example, a wafersupplier, such as, for example, SunEdison, may process a test or primesilicon wafer with a porous detach layer covered on one side by a thinepitaxial layer of silicon and a thick layer of oxide, ready for ox-oxbonding. Thus forming an Ox-dCS, an oxide topped detachable carriersubstrate. The wafer stack manufacturer, for example Intel or Samsung,utilizes the Ox-dCS in a stack process flow with a detach step, and thenmay return the used Ox-dCS to SunEdison for recycle or reclaim.

The flow presented in U.S. Pat. No. 8,273,610, FIG. 83 (A to K) usesoxide as isolation between stratum-2 1710 and stratum-3 1712. Forexample, FIG. 17 includes isolation layer 8301 for vertical electricalisolation, as well as 1602 of FIG. 16K.

Alternative options exist for the formation of vertical isolationincluding the use of deep implant, and there are device options thatmight not require isolation at all. Next are some embodiments for theseoptions.

An alternative embodiment is a memory structure such as disclosed in aU.S. Pat. No. 8,514,623, incorporated here by reference. In at leastFIG. 1A of the patent is an exemplary illustration the basic bit-cell ofthe memory. The memory utilizes a back bias 12 to keep two stable memorystates with one transistor bit cell. As illustrated in FIG. 18A, a backto back memory cells utilizing a unified back-bias are illustrated, thisallows an efficient use of stratum-2 1710 and stratum-3 1712 when formedin dual strata 1700 configuration.

Back bias is useful in many other circuits, such as, for example,Input/Output cells, linear circuits and sometimes to mitigate increasingprocess variability, as has been advocated by Open-Silicon with theirVanMax IP. FIG. 18B provides an exemplary illustration of N-channel andP-channel transistors each with its own back bias and these could be ondual strata 1700 as each transistor is isolated with its own back biaswhile the deep N well and or the p-substrate could be shared.

Fin-Fet, also called Tri-Gate transistor, generally are designed to befully depleted transistors. These transistors could be used on bothstratum-2 1710 and stratum-3 1712 and may be formed as a dual strata1700—see FIG. 18C, as their structure prevents any link to the substrateand accordingly they could share the substrate.

SuVolta, a start-up corporation, proposes a four doping-layer transistorstructure to reduce power with-out the use of Fin-Fet. By multi-layer ofdoping the transistor is designed to avoid leakage to the substrate.These transistors could be processed on both stratum-2 1710 andstratum-3 1712 and may be formed as a dual strata 1700—see FIG. 18D, astheir structure prevents any link to the substrate and accordingly theycould share the substrate.

There many design choices, including selection of process flow andcircuit architectures to allow effective use of stratum-2 1710 andstratum-3 1712 and formed as a dual strata 1700, including displacementbetween functions that could interfere, use of back bias or otherimplant based active isolation schemes, and local or global isolationstructures such as oxide or field shield regions or plates/layers.

Vertical isolation between Stratum-2 and Stratum-3 devices may be amatter of design, layout and process flow choices. An oxide layer and/orregions may provide some isolation between stratum-2 devices fromstratum-3 devices, and may include process that may include, forexample, an SOI donor wafer/substrate, the donor wafer/substrate maystart as a bulk silicon wafer and utilize an oxygen implantation andthermal anneal to form a buried oxide layer, such as, for example, theSIMOX process (i.e., separation by implantation of oxygen) or anMLD-SIMOX (modified low dose SIMOX) approach such as DK Sandana, or adouble layer transfer with oxide deposition in between to form dualstrata layer. Furthermore, for example, a pn junction may be formedbetween the vertically stacked transistors and may be biased. Also, asilicon-on-replacement-insulator technique may be utilized for the firstformed dummy transistors wherein a buried SiGe layer may be selectivelyetched out and refilled with oxide, thereby creating islands ofelectrically isolated silicon, similar to the 2D process known asSioN—‘Silicon on Nothing’. Vertical isolation may be obtained somewhatnaturally from a structure in one or more of a stratum-2 or stratum-3device, for example, the buried back-bias layer/regions of a ZenoSemiconductor NVM cell, a deep implanted layer or region, biased orun-biased as required between stratum-2 and stratum-3. Verticalisolation may occur due to placement of stratum-2 and stratum-3 devices,for example, a layout rule could require no high speed logic overanother high speed logic cell or region, but may allow a memory to beover the logic cell or region.

Additional embodiments are device structures that leverage this frontand back layer processing to enable effective device structuresincluding vertical device options. Vertical devices may include, forexample, memory (V-NAND, V-RRAM, Bi-ristor) as well as devices such asGate All Around transistors, vertical junction-less transistors,nano-wire, CNT, vertical bipolar, and so on. Some vertical structuresand devices may be found in at least incorporated reference U.S. Pat.No. 8,273,610.

Currently there are a few non-volatile memory architectures for 3D NANDutilizing poly silicon and floating gate or charge trap (nitride-SONOS)structure. Those could modified to be built utilizing monocrystallinechannel and benefiting with process flows allowing access to both sidesof the vertical structure, such as found in the use of stratum-2 1710and stratum-3 1712 and formed as a dual strata 1700.

In some embodiments ion cut could be used for the layer transfer fromthe donor wafer. Accordingly there are device choices for stratum-3 1712that would be less sensitive to the potential ion cut damage andpotential exposure to Stratum-2 processing. Such could be:

1. Circuits that use older technology node

2. Input Output circuit

3. Memory circuit such as presented in U.S. Pat. No. 8,514,623

4. Buffers, repeater and drivers

5. Resistive Random Access Memory (RRAM) select device

6. Image sensors

7. Clock and clock distribution networks, buffers

8. Non-volatile memory, for example, such as Zeno Semiconductor'snon-volatile RAM cell and technology, found in at least U.S.

9. Programming and/or select and/or load transistors and/or load devicesfor memory and/or programmable interconnect, for example, RRAM,anti-fuses, SRAM, flash.

10. Low Vt devices

11. Power devices

12. Low cost, older node devices,

13. Redundancy devices

14. Redundancy for yield improvement, which may include yield testing

15. Testing circuitry for example, scan chains and overhead such as JTAG

16. Optical drivers.

Recent release of a precision alignment Fusion Bonder machine fromcompanies such as EV Group allows very accurate and precise alignedbonding of a transferred layer to the target wafer. In U.S. Pat. No.8,273,610 the use of repeating structures has been suggested. These newbonders allow a better than 200 nm alignment accuracy and precision. Inthese cases there may be no need to use repeating structures, andstratum-2 1710 and stratum-3 1712 and/or formed as dual strata 1700could be most any circuit design and layout choice.

Yet, connecting dual strata 1700 to the underlying circuit of the basewafer 880 could use the two connection strips (generally orthogonal)described and a via that is aligned in one direction according to thealignment mark in the underlying target wafer 880 and in the otherdirection according to the alignment mark of the transferred layercarrying dual strata 1700, as has been described in at least U.S. Pat.No. 8,273,610 in reference to at least FIG. 80. These alignment schemesusing connection strips and an innovative via alignment scheme has beenpresented in U.S. Pat. No. 8,273,610 in reference to other figures suchas FIG. 79, FIG. 77 and others.

This process flow for constructing dual strata 1700, and precise bondingonto a target wafer with innovative connection as been hereby described,opens up many circuit, device and business options. It opens up optionsto use multiple vendors, multiple manufacturing sites/locations (fabs),and multiple process nodes in constructing an end product device. Itcould allow mixing of custom-made strata with standard-made strata. Itcould also support mixing of different base materials and crystals in amonolithic end product device. All of these heterogeneous integrationsmay enjoy an extremely rich vertical connectivity.

This opens up opportunity to build structures, for example such as dualstrata 1700, independently that per case which could be integrated withrich connectivity and low cost into a target wafer. For example, suchas:

1. Debug structure. This structure would be used for development andyield ramp up of new designs. In these cases there might be a need tocollect and test many device internal nodes while operating the device.These extra scan detect capture and analyze circuits need rich/denseconnections to the target wafer and would only be needed at the earlyphase of product development and ramp up. It would be desired to havesuch extra circuits at this early phase but then remove it at the highvolume production phase to keep the cost of the end device low. Such hasbeen described in U.S. Pat. No. 8,273,610 in reference to at least FIG.235 to FIG. 238.2. Yield repair. A redundancy stratum could be built as has beendescribed in U.S. Pat. No. 8,273,610 in reference to at least FIG. 119to FIG. 125. These could be used, for example, for wafers that show lowyield, for applications that need redundancy, or for transient randomerror mitigation.3. Power reduction. There are known techniques to produce a circuitfunction performing the same function at lower power. A good example isreplacing a processor based implementation with direct circuitimplementations. Prof. Bob Brodersen of the U. C. Berkeley WirelessResearch Center has published multiple papers on the subject. The targetwafer in many cases would carry the processor based implantation to meetthe time to market requirement. The direct implementation could be builton a stratum-2 1710 and/or a stratum-3 1712 (if both then a dual strata1700) and bonded on the target wafer to provide device options withreduced power (due to the direct design impletmentation).4. Extended memory options. In some devices there might be a value inoffering options for extended memories. Those could be built onstratum-2 1710 and/or stratum-3 1712 (if both then a dual strata 1700)and connected to the base/target device to extend memory. A customizableembedded memory terrain may also be included.5. Extended compute options. In some computer systems it might bedesirable to offer alternatives with more cores or more synapses. Addinglayers of stratum-2 1710 and/or stratum-3 1712 (if both then dual strata1700) could be an effective in forming and offering scalable computesystems.6. Add configurable logic terrain. Adding layers of stratum-2 1710and/or stratum-3 1712 (if both then dual strata 1700) which compriseconfigurable logic could add flexibility to overcome some limitation ofthe underlying system or allow to add an enhancement includingcustomized enhancement.7. Add Inputs, Outputs and/or Memories to an underlying configurabledevice such as an FPGA or Gate Array as described in at least U.S. Pat.No. 8,273,610 in reference to at least FIG. 11 (A to F).8. Add programmable interconnect above a target wafer that may include acontinuous logic terrain to construct a 3D FPGA. Stratum-2 and stratum-3may include programming, isolation, select switch devices and a memorystorage such as RRAM, or stratum-2 and stratum-3 may include a directswitch programmable interconnect such as anti-fuses with programming andisolation transistors.9. Add an image sensor with integrated pixel electronics, compressioncircuitry, fast memory, signal amplifier, and other processing/controlcircuits. The image sensor may include one or many wavelengths (forexample, as disclosed in at least U.S. Pat. Nos. 8,283,215 and8,163,581, incorporated herein by reference), and may be placed onstratum-3 with supporting circuitry on stratum-2 and in the targetwafer.10. Ultra-scale integration may be achieved by combining some of theabove options. For example, a dual strata of redundant logic may bestacked with one or more dual strata of memory (may mix volatile dualstrata with non-volatile dual strata), and may be combined with dualstrata or stratum of sensors, analog, I/O (electrical and/or optical),and so forth.

This also opens up opportunity for testing and opportunities forrepairing various components of the 3D stack. For example, as a matterof design and manufacturing choice, functional testing of the targetwafer may be done before the target wafer is bonded to the dual strata.Furthermore, the dual strata layer may be tested (at least partially)prior to bonding to the target wafer, most easily the stratum-2 devices;however, by design and manufacturing choice, connections to stratum-3devices (TDSC-Thru Dual Strata Connection) may be made at the time ofstratum-2 interconnection, depending on the type of contact (direct tostratum-3 device junctions, type of stratum-3 device, and preexistingstratum-3 device interconnect (such as local interconnect, pre-madeinterconnect with hi-temp material, etc.). Thus, testing in the 3DICstack flow may be performed at various stages within the flow, not justat the end, and may also test for different types or locations ofdefects at different points/steps in the overall flow. Defects may alsobe repaired at different points/steps in the overall flow.

After bonding of the dual strata to the target wafer, and TLVs are madeconnecting stratum-2 and stratum-3 devices to the interconnect of thetarget wafer, a connection test may be performed to find any connectionfaults, for example, dual-strata-to-target wafer connection faults. Aspecial probe connection may be designed and formed, for example, on thestratum-3 interconnect or a stacked bond pad from the target wafer upthru the dual strata, or test wafer backside connections may be formedand utilized. These special connections may also provide power to one ormore portions of the stack being tested. Wireless connections, such asinductive coupling or NFC, may also be employed. When connection faultsare found, they can be location logged and then the stack may bereturned to processing in a rework of the faulty connection(s). Forexample, e-Beam and/or laser etching and deposition may be employed tocorrect the connection faults.

There are additional options to bond and connect the transferred layerof dual strata 1700:

1. Bond oxide to oxide and etch via, which could be called through layervia (TLV) or through silicon via (TSV), through the transferred layer ofstratum-2 1710 and/or stratum-3 1712 (if both then dual strata 1700) toland on a landing strip as described in at least U.S. Pat. No. 8,273,610in reference to at least FIG. 80, then process at least one overlyinginterconnection layer which will include the strip to connect the via tothe stratum-2 1710 and/or stratum-3 1712 (if both then dual strata 1700)circuits.2. Bond metal to metal (or hybrid bonding) and have a connection paththrough the transferred layer of stratum-2 1710 and/or stratum-3 1712(if both then dual strata 1700) to the top as described in at least U.S.Pat. No. 8,273,610 in reference to at least FIG. 94 (A-C). At the topproper alignment would then complete the connection to the stratum-21710 and/or stratum-3 1712 (if both then dual strata 1700) circuits.3. Bond metal to metal (or hybrid bonding) and have a connection paththrough the transferred layer of stratum-2 1710 and/or stratum-3 1712(if both then dual strata 1700) as described in at least U.S. Pat. No.8,273,610 in reference to at least FIG. 155 (A-C).

The stratum-2 1710 and/or stratum-3 1712 (if both then dual strata 1700)circuits could comprise the additional support structures to help removethe internal accumulated heat. This could comprise the heat removalpaths leveraging the copper connection providing power to the stratum-21710 and/or stratum-3 1712 (if both then dual strata 1700) circuits, anembedded heat spreader for the stratum-2 1710 and/or stratum-3 1712 (ifboth then dual strata 1700) circuits and thermal contacts that may beelectrically non-conducting to transistors which may have a poor thermalpath. These and other heat removal and spreading techniques have beendescribed with more detail in U.S. Pat. No. 8,803,206 which isincorporated herein by reference.

This opens up opportunity to build structures, for example, that may bea combination of sequential and parallel 3DIC processing. For example,an exemplary stack may be constructed by the methods herein to have 2dual strata formed on top and connected to a target wafer, thus formingStack A. At the same manufacturing site as for Stack A, or a differentone, a second exemplary stack may be constructed by the methods hereinto have 2 dual strata formed on top and connected to a second targetwafer, thus forming Stack B. Stack A and Stack B may have similar ordiffering compositions of functions and strata. At the samemanufacturing site as for Stack A, or as for Stack B, or a differentfrom A or B one, Stack A and Stack B may be connected to each otherforming a super system. The connections between Stack A and Stack may beformed by back to back hybrid bonding, or other well-known methods suchas TSV. They may be placed on an interposer and connected to each otherand perhaps ancillary devices. They may be back-back bonded with no thruthe backside electrical connections other than a common body (or not ifox-ox bonded) and wired bonded connections may be made between thestacks, such as an I/O of Stack B being connected to an I/O of Stack A.This approach may be useful for constructing memories and for redundancy(memory, logic, and system).

These inventions provide many benefits to all type of electronic basedproducts. And especially for products that target mobility or need toallow high integration at small volume and low power. Some of theseapplications have been described in at least U.S. Pat. No. 8,273,610 inreference to at least FIG. 156 and FIG. 91.

FIGS. 19A to 19K describe an exemplary process flow utilizing a carrierwafer or a holder wafer or substrate wherein CMOS transistors may beprocessed on two sides of a donor wafer. PMOS and NMOS transistors maybe formed on each of the two sides or NMOS on one side and PMOS on theother, and then the two sided structure (NMOS on top of PMOS or CMOS ontop of CMOS, or a combination thereof) donor wafer may be transferred toan target or acceptor wafer/substrate with pre-processed circuitry. Withreference to descriptions herein, this may be the formation of stratum-21710 and stratum-3 1712 devices (thus forming a dual strata 1700), whichmay be layer transferred and connected to a target wafer/substrate 808.Description of target wafer/substrate 808 may be found in at leastreferenced U.S. Pat. No. 8,273,610. State of the art CMOS transistorsand compact 3D library cells may be constructed with methods that may besuitable for 3D IC manufacturing. The exemplary process flow of FIGS.19A to 19K describes CMOS on one side and CMOS on the other, as well asthe commonly employed gate-last HKMG approach, and depicts anoxide-based vertical isolation, for simplicity. In the example, ion-cutis utilized for the layer transfer out of a donor wafer/substrate anddamage/stress splitting technique for layer transfer out of a carrierwafer/substrate. However, many types of devices as mentioned herein maybe formed on one side or both sides of the donor wafer and many types oflayer transfer techniques as mentioned herein may be applied, accordingto manufacturing and technical choices. Some similarities and otherdetails with the processing flow now presented may be found herein andin referenced and incorporated documents; for example, in at least FIGS.70-80 and associated specification of U.S. Pat. No. 8,273,610.

As illustrated in FIG. 19A, a Silicon On Oxide (SOI) donor wafersubstrate 1900 may be processed in the typical state of the art CMOSHKMG gate-last manner up to the step prior to where CMP exposure of thepoly-crystalline silicon dummy gates takes place. SOI donor wafersubstrate 1900, the buried oxide (i.e., BOX) 1901, the thin siliconlayer 1902 of the SOI wafer, the stratum-3 shallow trench isolation(STI) 1903 among stratum-3 CMOS transistors, the ‘dummy’poly-crystalline silicon 1904 and gate dielectric 1905 of the stratum-3NMOS dummy gates, stratum-3 NMOS source and drains 1906, stratum-3 NMOStransistor channel 1907, the ‘dummy’ poly-crystalline silicon 1954 andgate dielectric 1955 of the stratum-3 PMOS dummy gates, stratum-3 PMOSsource and drains 1956, stratum-3 PMOS transistor channel 1957, andstratum-3 CMOS interlayer dielectric (ILD) 1908 are shown in thecross-section illustration. These structures of FIG. 19A illustrate thesubstantial completion of the first phase of stratum-3 CMOS transistorformation. The thermal cycles of the stratum-3 CMOS HKMG process up tothis point in the flow may be adjusted to compensate for later thermalprocessing.

As illustrated in FIG. 19B, a layer transfer demarcation plane/layer(shown as dashed line) 1999 may be formed in SOI donor wafer substrate1900 by hydrogen implantation 1910 or other methods as previouslydescribed (for example, porous layer or layers) in at least herein andthe incorporated documents.

As illustrated in FIG. 19C, oxide 1916 may be deposited onto carrierwafer/substrate 1920 and then both the SOI donor wafer substrate 1900and carrier wafer/substrate 1920 may be prepared for wafer bonding aspreviously described in incorporated references, and then may be oxideto oxide bonded together at interface 1914. Carrier wafer/substrate 1920may also be called a carrier or holder substrate, and may be composed ofmono-crystalline silicon, or other materials suitable for the thermalstresses and contamination requirements of the process flow.

As illustrated in FIG. 19D, the portion of the SOI donor wafer substrate1900 that may be below the layer transfer demarcation plane 1999 may beremoved by cleaving or other processes as previously described hereinand in at least the incorporated documents, such as, for example,ion-cut or other methods. The remaining donor wafer layer 1900′ may bethinned by chemical mechanical polishing (CMP) and surface 1922 may beprepared for stratum-2 transistor formation. Damages from the ion-cutprocessing may be repaired by at least methods disclosed herein and inthe incorporated documents; for example, laser annealing, thermalannealing, SiGen Corporation's epi-smoothing, etc., depending on thethermal budget of the thin silicon layer 1902 partially formedtransistors and devices.

As illustrated in FIG. 19E, donor wafer layer 1900′ may be processed inthe typical state of the art CMOS HKMG gate last processing manner up tothe step prior to where CMP exposure of the poly-crystalline silicondummy gates takes place to form the stratum-2 CMOS transistors withdummy gates. The stratum-2 CMOS transistors may be precisely aligned atstate of the art tolerances to the stratum-3 CMOS transistors as aresult of the shared substrate possessing the same alignment marks. Forexample, an alignment error of less than about 40 nm, less than about 20nm, less than about 10 nm, less than about 5 nm. Carrier wafer/substrate1920, oxide 1916, BOX 1901, the thin silicon layer 1902 of the SOIwafer, the shallow trench isolation (STI) 1903 among stratum-3 CMOStransistors, the poly-crystalline silicon 1904 and gate dielectric 1905of the stratum-3 NMOS dummy gates, stratum-3 NMOS source and drains1906, the stratum-3 NMOS transistor channels 1907, the poly-crystallinesilicon 1954 and gate dielectric 1955 of the stratum-3 PMOS dummy gates,stratum-3 PMOS source and drains 1956, the stratum-3 PMOS transistorchannels 1957, and the stratum-3 CMOS interlayer dielectric (ILD) 1908,donor wafer layer 1900′, the shallow trench isolation (STI) 1933 amongstratum-2 CMOS transistors, the poly-crystalline silicon 1934 and gatedielectric 1935 of the stratum-2 NMOS dummy gates, stratum-2 NMOS sourceand drains 1936, the stratum-2 NMOS transistor channels 1937, thepoly-crystalline silicon 1994 and gate dielectric 1995 of the stratum-2PMOS dummy gates, stratum-2 PMOS source and drains 1996, the stratum-2PMOS transistor channels 1997, and the stratum-2 CMOS interlayerdielectric (ILD) 1938 are shown in the exemplary cross sectionillustration. A high temperature anneal may be performed to activateboth the stratum-2 and stratum 3 transistor dopants. These structures ofFIG. 19E illustrate substantial completion of the first phase ofstratum-2 CMOS transistor formation. The stratum-2 CMOS transistors maynow be ready for typical state of the art gate-last transistor formationcompletion.

As illustrated in FIG. 19F, the stratum-2 CMOS ILD 1938 may be chemicalmechanically polished to expose the top of the stratum-2 CMOSpoly-crystalline silicon dummy gates, and the dummy gates may then beremoved by etching. The stratum-2 PMOS devices may be hard masked-offand stratum-2 hi-k NMOS gate dielectric 1940 and the stratum-2 NMOSspecific work function metal gate 1941 may be deposited. The stratum-2NMOS devices may be hard masked off and stratum-2 hi-k PMOS gatedielectric 1970 and the stratum-2 PMOS specific work function metal gate1971 may be deposited. An aluminum fill 1942 may be performed and themetal chemical mechanically polished. A low temperature stratum-2dielectric layer 1939 may be deposited and the typical gate 1943 andsource/drain 1944 contact formation and metallization may now beperformed to connect to and among the stratum-2 CMOS transistors.Partially formed stratum-2 inter layer via (ILV) 1947 may belithographically defined, plasma/RIE etched, and metallization formed.Oxide layer 1948 may be deposited to prepare for ox-ox bonding.Furthermore, the gate dielectric on transistors may have differentdielectric permittivities than silicon dioxde. The gate dielectricpermittivity of the second layer transistors, such as Stratum-2 and/orStratum-3 transistors/devices, may be different than the gate dielectricpermittivity of the first layer (base/substrate/or lower in the stack)transistors.

As illustrated in FIG. 19G, a damage plane or layer (shown as dashedline) 1998 may be formed in carrier wafer/substrate 1920 by opticalmeans 1971, for example a two-phonon exposure with lasers, wherein thedepth of the two-phonon interaction may be controlled with optics.Silicon to silicon bonds may be broken in a 2-phonon interaction,forming a layer or plane of silicon vacancies and silicon interstitialatoms (sometimes called interstitial vacancy pairs). Optical means 1971may be employed thru carrier wafer/substrate 1920 to minimize 1-phononinteractions with doped regions and metal layers, or may be employedthru the processed layers (from ‘below in the FIG. 19G context, notshown), or a combination of both. Other layer transfer techniques, suchas the porous layer such as ELTRAN, etc. described at least herein, maybe utilized for the carrier wafer/substrate 1920 and/or damage plane orlayer 1998.

As illustrated in FIG. 19H, the donor wafer surface at oxide layer 1948and top oxide surface of acceptor or target wafer/substrate 1988 withacceptor wafer metal connect strip 1950 may be prepared for waferbonding as previously described and then low temperature (less thanapproximately 300° C.) aligned and oxide to oxide bonded at interface1951. The process temperature is preferred as low as possible tomitigate reconstitution of the interstitial vacancy pairs of damageplane or layer 1998 If the 2-phonon method is utilized). The acceptormetal strip and donor metal strip methodology, described in at leastFIGS. 71, 72-80 and associated specification of incorporated U.S. Pat.No. 8,273,610, and may employ a machine such as the EV Group Gemini FBXT, which may provide alignment of thick substrates to within 200 nm.Small acceptor squares of maximum misalignment dimensions may also beutilized to connect the donor wafer/substrate metal TLV to the acceptorwafer metallization, such as described in at least FIG. 75 of the abovepatent.

As illustrated in FIG. 19I, the portion of the carrier or holder wafer1920 that may be above damage plane or layer 1998 may be removed bycontrolled stress methods. A polymer or co-polymer layer 1973 may bedeposited on carrier or holder wafer 1920 (shown in FIG. 19H forclarity). Polymer or co-polymer layer 1973 may also be deposited on thebackside acceptor or target substrate 1988 (not shown). Thethickness(es) of polymer or co-polymer layer 1973 on either side of theentire structure may be tuned to provide the proper stress levels tocleave at damage plane or layer 1998 when exposed to a thermal stress.Polymer or co-polymer layer 1973 may incorporate a release layer tofacilitate an easy release from whichever surface it was applied to. Athermal stress, for example, immersion or spray of LN2 (Liquid Nitrogen)may be used as a stress for cleaving. Details and demonstration of thepolymer stress and optical vacancy creation cleaving methods for siliconwafering of an ingot may be found with Siltectra GmbH atwww.siltectra.com and patent disclosures of Lukas Lichtensteiger, suchas US Patent Application Publication 2011/0259936 and internationalpublication WO2014005726. These stress techniques may be applied toother process flows within the incorporated references; for example, atleast FIGS. 81 and 82 and associated specification of U.S. Pat. No.8,273,610. The remaining layer of the carrier or holder wafer 1920remaining on the structure attached to oxide layer 1916 may be removedby chemical mechanical polishing (CMP) to or into oxide layer 1916. Withconventional sidewall and backside protection, chemical means may alsobe employed, for example, warm KOH, to remove remaining portions of thecarrier wafer/substrate 1920. The remaining bulk of carrierwafer/substrate 1920 may be recycle or reclaimed for additional uses,such as reuse as a carrier wafer. The dual strata is transferred andbonded to the target wafer and the stratum-3 CMOS transistors may be nowready for typical state of the art gate-last transistor formationcompletion.

As illustrated in FIG. 19J, oxide 1916 and the stratum-3 CMOS ILD 1908may be chemical mechanically polished to expose the top of the stratum-3CMOS dummy gates. The stratum-3 PMOS areas may be hard masked off andthe stratum-3 NMOS dummy gates may then be removed by etching. Astratum-3 hi-k gate dielectric 1960 and a stratum-3 NMOS specific workfunction metal gate 1961 may be deposited. The stratum-3 NMOS areas maythen be hard masked off (after PMOS hard mask removed) and the stratum-3PMOS dummy gates may then be removed by etching. A stratum-3 hi-k gatedielectric 1950 and a stratum-3 PMOS specific work function metal gate1951 may be deposited. An aluminum fill 1962 may be performed and themetal chemical mechanically polished. A low temperature dielectric layer1969 may be deposited and the typical gate 1963 and source/drain 1964contact formation and metallization may now be performed to connect toand among the stratum-3 CMOS transistors. Partially formed stratum-3CMOS inter layer via (ILV) 1967 may be lithographically defined,plasma/RIE etched, and metallization formed, thus electricallyconnecting stratum-3 CMOS ILV 1967 to stratum-2 CMOS ILV 1947.

As illustrated in FIG. 19K, dual strata oxide 1970 may be deposited andplanarized. Thru layer via (TLV) 1972 may be lithographically defined,plasma/RIE etched, and metallization formed. Alignment of TLV 1972 maybe based on both the target wafer alignment marks and the dual strataalignment marks (not shown). TLV 1972 electrically couples the NMOStransistor layer metallization to the acceptor or target substrate 1988at acceptor wafer metal connect strip 1950. A topmost metal layer, at orabove oxide 1970, of the layer stack illustrated may be formed to act asthe acceptor wafer metal connect strips for a repeat of the aboveprocess flow to stack another preprocessed thin mono-crystalline siliconlayer of CMOS on top of CMOS transistors.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 19A through 19K are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, the transistor layers oneach side of BOX 1901 may include many combinations and types ofsemiconductor devices. Additionally, the above process flow may also beutilized to construct gates of other types, such as, for example, dopedpoly-crystalline silicon on thermal oxide, doped poly-crystallinesilicon on oxynitride, or other metal gate configurations, as ‘dummygates,’ perform a layer transfer of the thin mono-crystalline layer,replace the gate electrode and gate oxide, and then proceed with lowtemperature interconnect processing. Moreover, that other transistortypes may be possible, such as, for example, RCAT, FinFet, andjunction-less. Further, the donor wafer layer 1900′ in FIG. 19D may beformed from a bulk mono-crystalline silicon wafer with CMP to the NMOSjunctions and oxide deposition in place of the SOI wafer discussed.Additionally, the SOI donor wafer substrate 1900 may start as a bulksilicon wafer and utilize an oxygen implantation and thermal anneal toform a buried oxide layer, such as, for example, the SIMOX process(i.e., separation by implantation of oxygen), or SOI donor wafersubstrate 1900 may be a Germanium on Insulator (GeOI) wafer. The layertransfer of FIG. 19F-191 may be effected by forming a layer demarcationplane in carrier or holder wafer 1920 by hydrogen implantation. Stresslayers, embedded & raised source/drains, and other conventional HKMGrelated techniques may be utilized in the exemplary process flow withinthe temperature constraints of each step. Other schemes may be employedto create stratum-2 to stratum-3 connections, for example, a via may beetched during the stratum-3 interconnect formation (or TLV connectionvia etch, stopping on a stratum-2 landing pad for that case) that wouldtraverse both stratum-3 and stratum-2 STI's and isolation layers toconnect to a stratum-2 landing pad metal structure. Many othermodifications within the scope of the invention will suggest themselvesto such skilled persons after reading this specification. Thus the scopeof the invention is to be limited only by the appended claims.

As illustrated in FIG. 20 (FIG. 20), exemplary 3DIC device 2000 may beconstructed with many of the process flow options and sub-devicesdescribed at least herein and in the incorporated references. Exemplary3DIC device 2000 may also be called a 3DIC system, or a 3D semiconductordevice, or a 3D stacked device, or a monolithic 3D device. 3DIC device2000 may include target wafer/substrate 2088, and at least one dualstrata 2090, which may include target wafer to dual strata bond layer2082 and 3DIC device protect layer 2076. Dual strata 2090 may overlaytarget wafer/substrate 2088. 3DIC device protect layer 2076 may includepassivation materials to protect the device and may include bond padopenings (not shown) for connection to external devices. 3DIC deviceprotect layer 2076 may include oxide or other bonding materials, inpreparation for bonding with another layer or 3DIC device/stack oranother dual strata or stratum. Target wafer/substrate 2088 may includedevice layer 2084 and metal interconnect layer or layers. Device layer2084 may include devices such as transistors, diodes, junctions, and soon and may include the definitions with respect to acceptor or target orbase wafer/substrate found herein and in the incorporated references.Device layer 2084 metal interconnect layer or layers may include targetwafer landing strip 2086, which may be called acceptor wafer metalconnect strip. Dual strata 2090 may include stratum-3 2030 and stratum-22020, and may include, depending on design, layout, device andmanufacturing engineering choices, vertical isolation regions 2008.Vertical isolation regions 2008 may cover most of the area betweenstratum-3 2030 and stratum-2 2020 and as such, may be a called a layer.Stratum-2 2020 may include stratum-2 device layer 2024 and stratum-2metal interconnect layer 2026. Stratum-2 device layer 2024 may includestratum-2 device regions 2022 and stratum-2 STI (Shallow TrenchIsolation) regions 2028. Stratum-2 device regions 2022 may includetransistors, such as CMOS MOSFETs or FinFets, and other device types asfound herein and known by one of ordinary skill in the art. Stratum-22020 may contribute/share structure, connection, electricalbias/signals, and so on to vertical isolation regions 2008 as dictatedby engineering and design choices. Stratum-2 metal interconnect layer2026 may include multiple layers of metal interconnect, vias, andisolation dielectric regions. Stratum-3 2030 may include stratum-3device layer 2034 and stratum-3 metal interconnect layer 2036. Stratum-3device layer 2034 may include stratum-3 device regions 2032 andstratum-3 STI regions 2038. Stratum-3 device regions 2032 may includetransistors, such as CMOS MOSFETs or FinFets, and other device types asfound herein and known by one of ordinary skill in the art. Stratum-32030 may contribute/share structure, connection, electricalbias/signals, and so on to vertical isolation regions 2008 as dictatedby engineering and design choices. Stratum-3 metal interconnect layer2036 may include multiple layers of metal interconnect, vias, andisolation dielectric regions. Stratum-3 2030 devices, for exampletransistors, may be electrically and/or thermally connected to stratum-22020 devices, for example transistors, thru the respective stratum metalinterconnect and dual strata inter layer via (ILV) 2092. Devicesresiding on or connected to dual strata 2090 may be electrically and/orthermally connected to target wafer/substrate 2088 devices, for exampletransistors, thru the respective stratum metal interconnect and thrulayer via (TLV) 2094. Stratum-2 STI regions 2028 and stratum-3 STIregions 2038 may be designed to physically connect to provide a fullyisolating vertical opening thru any conductive layers for conductivevertical connections such as ILV 2092 and TLV 2094. If verticalisolation regions 2008 are electrically isolating, this full connectionmay not be necessary.

As illustrated in FIG. 21 (FIG. 21), a flowchart of the major steps in a3DIC device formation flow utilizing a detachable donor substrate and adetachable carrier substrate is presented. 3DIC device 2000 of FIG. 20herein, for example, may be formed with this process flow.

A Si-dDS, a silicon topped detachable donor substrate, is provided andstratum-3 devices such as transistors may be processed thru the FEOL(Front End Of Line) in a conventional manner (potentially withcompensation for future thermal exposure during stratum-2 deviceprocessing) [step 2100]. A Si-dDS may be a prime silicon wafer with aporous detach layer covered on one side by an epitaxial layer of siliconas described herein.

The processed Si-dDS may be prepared for bonding and an Ox-dCS may beprepared for bonding, an oxide topped detachable carrier substrate.[step 2110]. An Ox-dCS may be a test or prime silicon wafer with aporous detach layer covered on one side by a thin epitaxial layer ofsilicon and a thick layer of oxide, ready for ox-ox bonding.

The processed and bonding prepared Si-dDS may be bonded to the bondingprepared an Ox-dCS. The alignment error between Si-dDS and the Ox-dCSmay be about 2 microns or less [step 2120]. The bonding may be oxide tooxide, but must be a type of bond strong enough to reliably survivesubsequent thermal processing and sheer forces, generally >1 J/cm².

The processed Si-dDS may be cleaved at or near the porous detach layerby methods described herein, and the remainder removed, thus leaving atransferred donor layer (TDL) attached to the Ox-dCS [step 2130]. TheTDL may include the FEOL processed stratum-3 devices, a verticalisolation layer if required, and an additional portion of donor wafermaterial. Depending on the cleave process utilized, the Ox-dCS porousdetach layer edge may be protected from the Si-dDS cleaving process (forexample, wax coatings, etc. if water jet cleave action).

The exposed surface of the TDL may be prepared for stratum-2 deviceprocessing [step 2140]. Processing may include CMP, laser anneals,oxidation, epi-smoothing and other processing as described herein asdictated by the engineering and device constraints of the FEOL stratum-3devices, and the needs of the desired stratum-2 devices.

Stratum-2 devices may be conventionally processed and formed, both FEOLand BEOL (Back End Of Line—contacts, metal interconnect, vias, and soon) thus forming a dual strata layer (DSL) attached to Ox-dCS [step2150]. As a matter of design and engineering choices, stratum-2 tostratum-3 ILVs may be partially formed at this point, or formed later.

The DSL top surface (stratum-3 side of DSL) may be prepared for bondingand the target wafer may be prepared for bonding [step 2160]. Targetwafer/substrate may include devices, transistors, metal interconnect,TLV landing strips or zones, and so on, as describe herein.

The DSL+Ox-dCS structure (DSL prepped surface) may be permanently bondedto the target wafer utilizing precision wafer bonding technology [step2170]. The DSL structure to target wafer/substrate structure alignmenterror may be less than about 200 nm, less than about 200 nm, less thanabout 500 nm. Smart alignment techniques, disclosed herein and inincorporated references, may be utilized.

The Ox-dCS may be cleaved at or near the porous detach layer by methodsdescribed herein, and the remainder removed, thus leaving the DSLattached to the target wafer. [step 2180]. The fragments of Ox-dCSremaining attached to the DSL may be removed, and the stratum-3replacement gate FEOL steps, if required, may be processed and formed.

Process and form interconnects, including stratum-3 to stratum-3(stratum-3 BEOL), stratum-3 to stratum-2 (ILV), stratum-3 or stratum-2to target wafer (TLV), target wafer to prep for above Stratum-3 (forexample, for bond pads or connect to another DSL or stack) [step 2190].Thus a 3DIC device, for example, such as illustrated in FIG. 20 herein,may be formed.

An embodiment of the invention may include various modification of theprocess flows described in at least U.S. Pat. No. 8,273,610 in relationto at least FIGS.: 70A-70F, 81A-81F, 82A-82G, 83A-83L. These flows maystart with a donor wafer which may go through a normal process flow toform a circuit layer which we could call stratum-3. The described flowsuggests the use of a ‘gate-replacement’ flow, also called ‘gate-last’flow for transistor formation, although other structures/techniques maybe utilized. The stratum-3 layer would be first transferred usingion-cut to a carrier wafer/substrate and then transferred on top of atarget wafer (also called base or acceptor wafer/substrate in somecircumstances). Once on top of the target wafer the dummy oxide and thedummy gate could be replaced with the gate last gate stack of, forexample, hafnium oxide and metal gate. This flow provides the advantagethat any damage caused by the ion-cut would be removed by thereplacement step. In an embodiment the replacement oxide and gate couldbe made with silicon oxide and poly gate which are in most cases cheaperand easier to process. So the repair of the ion-cut potential damage isnot a condition of having high-K metal gate process. It should be notedthat once stratum-3 is bonded on the target wafer the temperaturelimitation, generally restricted to less than 400° C., due to theunderlying structure does exist. Therefore, a special process should beused for the deposition of a high quality gate oxide. Furthermore, thedummy gate stack may be replaced after the ion-cut by other types ofgate stacks; for example, such as a grown or deposited oxide/dielectricwith a polysilicon/polycide electrode, or a grown or depositedoxide/dielectric with a tungsten electrode. Such processes have beenpresented in at least U.S. Pat. No. 8,273,610.

The challenge of aligning preformed or partially preformed planartransistors to the underlying layers and substrates may be overcome bythe use of repeating structures on the donor wafer or substrate and theuse of metal connect landing strips either on the acceptor wafer only oron both the donor and acceptor wafers. The metal connect landing stripsmay be formed with metals, such as, for example, copper or aluminum, andmay include barrier metals, such as, for example, TiN or WCo. Repeatingpatterns in one direction, for example, North to South repeats ofpreformed structures may be accomplished with the alignment scheme andmetal landing strips as described previously with reference to the FIG.33 of incorporated reference U.S. Pat. No. 8,273,610. The gate last HKMGprocess may be utilized to create a pre-processed donor wafer thatbuilds not just one transistor type but both types by utilizingalternating parallel strips or rows that may be the die width plusmaximum donor wafer to acceptor wafer misalignment in length.

Some embodiments of the invention may include alternative techniques tobuild IC (Integrated Circuit) devices including techniques and methodsto construct 3D IC systems. Some embodiments of the invention may enabledevice solutions with far less power consumption than prior art. Thedevice solutions could be very useful for the growing application ofmobile electronic devices and mobile systems such as, for example,mobile phones, smart phone, and cameras, those mobile systems may alsoconnect to the internet. For example, incorporating the 3D ICsemiconductor devices according to some embodiments of the inventionwithin the mobile electronic devices and mobile systems could providesuperior mobile units that could operate much more efficiently and for amuch longer time than with prior art technology.

Smart mobile systems may be greatly enhanced by complex electronics at alimited power budget. The 3D technology described in the multipleembodiments of the invention would allow the construction of low powerhigh complexity mobile electronic systems. For example, it would bepossible to integrate into a small form function a complex logic circuitwith high density high speed memory utilizing some of the 3D DRAMembodiments of the invention and add some non-volatile 3D NAND chargetrap or RRAM described in some embodiments of the invention. Mobilesystem applications of the 3DIC technology described herein may be foundat least in FIG. 156 of U.S. Pat. No. 8,273,610, the contents of whichare incorporated by reference.

Furthermore, some embodiments of the invention may include alternativetechniques to build systems based on integrated 3D devices includingtechniques and methods to construct 3D IC based systems that communicatewith other 3DIC based systems. Some embodiments of the invention mayenable system solutions with far less power consumption andintercommunication abilities at lower power than prior art. Thesesystems may be called ‘Internet of Things“, or IoT, systems, wherein thesystem enabler is a 3DIC device which may provide at least threefunctions: a sensing capability, a digital and signal processingcapability, and communication capability. For example, the sensingcapability may include a region or regions, layer or layers within the3DIC device which may include, for example, a MEMS accelerometer (singleor multi-axis), gas sensor, electric or magnetic field sensor,microphone or sound sensing (air pressure changes), image sensor of oneor many wavelengths (for example, as disclosed in at least U.S. Pat.Nos. 8,283,215 and 8,163,581, incorporated herein by reference),chemical sensing, gyroscopes, resonant structures, cantileverstructures, ultrasonic transducers (capacitive & piezoelectric). Digitaland signal processing capability may include a region or regions, layeror layers within the 3DIC device which may include, for example, amicroprocessor, digital signal processor, micro-controller, FPGA, andother digital land/or analog logic circuits, devices, and subsystems.Communication capability, such as communication from at least one 3DICof IoT system to another, or to a host controller/nexus node, mayinclude a region or regions, layer or layers within the 3DIC devicewhich may include, for example, an RF circuit and antenna or antennasfor wireless communication which might utilize standard wirelesscommunication protocols such as G4, WiFi or Bluetooth, I/O buffers andeither mechanical bond pads/wires and/or optical devices/transistors foroptical communication, transmitters, receivers, codecs, DACs, digital oranalog filters, modulators.

Energy harvesting, device cooling and other capabilities may also beincluded in the system. The 3DIC inventions disclosed herein and in theincorporated referenced documents enable the IoT system to closelyintegrate different crystal devices, for example a layer or layers ofdevices/transistors formed on and/or within mono or poly crystallinesilicon combined with a layer or layers of devices/transistors formed onand/or within Ge, or a layer of layers of GaAs, InP, differing siliconcrystal orientations, and so on. For example, incorporating the 3D ICsemiconductor devices according to some embodiments of the invention asor within the IoT systems and mobile systems could provide superior IoTor mobile systems that could operate much more efficiently and for amuch longer time than with prior art technology. The 3D IC technologyherein disclosed provides a most efficient path for heterogeneousintegration with very effective integration reducing cost and operatingpower with the ability to support redundancy for long field life andother advantages which could make such an IoT System commerciallysuccessful.

Alignment is a basic step in semiconductor processing. For most cases itis part of the overall process flow that every successive layer ispatterned when it is aligned to the layer below it. These alignmentscould all be done to one common alignment mark, or to some otheralignment mark or marks that are embedded in a layer underneath. Intoday's equipment such alignment would be precise to below a fewnanometers and better than 40 nm or better than 20 nm and even betterthan 10 nm. In general such alignment could be observed by comparing twodevices processed using the same mask set. If two layers in one devicemaintain their relative relationship in both devices—to fewnanometers—it is clear indication that these layers are one aligned eachto the other. This could be achieved by either aligning to the samealignment mark (sometimes called a zero mark alignment scheme), or onelayer is using an alignment mark embedded in the other layer (sometimescalled a direct alignment), or using different alignment marks of layersthat are aligned to each other (sometimes called an indirect alignment).

In this document, the connection made between layers of, generallysingle crystal, transistors, which may be variously named for example asthermal contacts and vias, Thru Layer Via (TLV), TSV (Thru Silicon Via),may be made and include electrically and thermally conducting materialor may be made and include an electrically non-conducting but thermallyconducting material or materials. A device or method may includeformation of both of these types of connections, or just one type. Byvarying the size, number, composition, placement, shape, or depth ofthese connection structures, the coefficient of thermal expansionexhibited by a layer or layers may be tailored to a desired value. Forexample, the coefficient of thermal expansion of the second layer oftransistors may be tailored to substantially match the coefficient ofthermal expansion of the first layer, or base layer of transistors,which may include its (first layer) interconnect layers.

Base wafers or substrates, or acceptor wafers or substrates, or targetwafers substrates herein may be substantially comprised of a crystallinematerial, for example, mono-crystalline silicon or germanium, or may bean engineered substrate/wafer such as, for example, an SOI (Silicon onInsulator) wafer or GeOI (Germanium on Insulator) substrate. Similarly,donor wafers herein may be substantially comprised of a crystallinematerial and may include, for example, mono-crystalline silicon orgermanium, or may be an engineered substrate/wafer such as, for example,an SOI (Silicon on Insulator) wafer or GeOI (Germanium on Insulator)substrate, depending on design and process flow choices.

While mono-crystalline silicon has been mentioned as a transistormaterial in this document, other options are possible including, forexample, poly-crystalline silicon, mono-crystalline germanium,mono-crystalline III-V semiconductors, graphene, and various othersemiconductor materials with which devices, such as transistors, may beconstructed within. Moreover, thermal contacts and vias may not bestacked in a vertical line through multiple stacks, layers, strata ofcircuits. Thermal contacts and vias may include materials such as sp2carbon as conducting and sp3 carbon as non-conducting of electricalcurrent. Thermal contacts and vias may include materials such as carbonnano-tubes. Thermal contacts and vias may include materials such as, forexample, copper, aluminum, tungsten, titanium, tantalum, cobalt metalsand/or silicides of the metals. First silicon layers or transistorchannels and second silicon layers or transistor channels may be may besubstantially absent of semiconductor dopants to form an undoped siliconregion or layer, or doped, such as, for example, with elemental orcompound species that form a p+, or p, or p−, or n+, or n, or n-siliconlayer or region. A heat removal apparatus may include an externalsurface from which heat transfer may take place by methods such as aircooling, liquid cooling, or attachment to another heat sink or heatspreader structure. Furthermore, raised source and drain contactstructures, such as etch and epi SiGe and SiC, and implanted S/Ds (suchas C) may be utilized for strain on a transistor channel to enhancecarrier mobility and may provide contact resistance improvements Damagefrom the processes may be optically annealed. Strain on a transistorchannel to enhance carrier mobility may be accomplished by a stressorlayer or layers as well.

In this specification the terms stratum, tier or layer might be used forthe same structure and they may refer to transistors or other devicestructures (such as capacitors, resistors, inductors) that may liesubstantially in a plane format and in most cases such stratum, tier orlayer may include the interconnection layers used to interconnect thetransistors on each. In a 3D device as herein described there may atleast two such planes called tier, or stratum or layer.

In a 3DIC system stack, each layer/stratum may include a differentoperating voltage than other layers/stratum, for example, one stratummay have Vcc of 1.0 v and another may have a Vcc of 0.7 v. For example,one stratum may be designed for logic and have the appropriate Vcc forthat process/device node, and another stratum in the stack may bedesigned for analog devices, and have a different Vcc, likelysubstantially higher in value—for example, greater than 3 volts, greaterthan 5 volts, greater than 8 volts, greater than 10 volts. In a 3DICsystem stack, each layer/stratum may include a different gate dielectricthickness than other layers/stratum. For example, one stratum mayinclude a gate dielectric thickness of 2 nm and another 10 nm. Thedefinition of dielectric thickness may include both a physicaldefinition of material thickness and an electrically ‘effective’thickness of the material, given differing permittivity of thematerials. In a 3DIC system stack, each layer/stratum may includedifferent gate stack materials than other layers/stratum. For example,one stratum may include a HKMG (High k metal gate) stack and anotherstratum may include a polycide/silicon oxide gate stack. In a 3DICsystem stack, each layer/stratum may include a different junction depththan other layers/stratum. For example, the depth of the junctions mayinclude a FET transistor source or drain, bipolar emitter and contactjunctions, vertical device junctions, resistor or capacitor junctions,and so on. For example, one stratum may include junctions of a fullydepleted MOSFET, thus its junction depth may be defined by the thicknessof the stratum device silicon to the vertical isolation, and the otherstratum may also be fully depleted devices with a junction depth definedsimilarly, but one stratum has a thicker silicon layer than the otherwith respect to the respective edges of the vertical isolation. In a3DIC system stack, each layer/stratum may include a different junctioncomposition and/or structure than other layers/stratum. For example, onestratum may include raised source drains that may be constructed from anetch and epitaxial deposition processing, another stratum in the stackmay have implanted and annealed junctions or may employ dopantsegregation techniques, such as those utilized to form DSS Schottkytransistors.

It should be noted that one of the design requirements for a monolithic3D IC design may be that substantially all of the stacked layers and thebase or substrate would have their respective dice lines (may be calledscribelines) aligned. As the base wafer or substrate is processed andmultiple circuits may be constructed on semiconductor layers thatoverlay each other, the overall device may be designed wherein eachoverlaying layer would have its respective dice lines overlying the dicelines of the layer underneath, thus at the end of processing the entirelayer stacked wafer/substrate could be diced in a dicing step. There maybe test structures in the streets between dice lines, which overall maybe called scribelanes or dicelanes. These scribelanes or dicelanes maybe 10 um wide, 20 um wide, 50 um wide 100 um wide, or greater than 100um wide depending on design choice and die singulation processcapability. The scribelanes or dicelanes may include guard-ringstructures and/or other die border structures. In a monolithic 3D designeach layer test structure could be connected through each of theoverlying layers and then to the top surface to allow access to these‘buried’ test structure before dicing the wafer. Accordingly the designmay include these vertical connections and may offset the layer teststructures to enable such connection. In many cases the die borderscomprise a protection structure, such as, for example, a guard-ringstructure, die seal structure, ESD structure, and others elements.Accordingly in a monolithic 3D device these structures, such as guardrings, would be designed to overlay each other and may be aligned toeach other during the course of processing. The die edges may be sealedby a process and structure such as, for example, described in relationto FIG. 183C of incorporated U.S. Pat. No. 8,273,610, and may includeaspects as described in relation to FIG. 183A and 183B of samereference. One skilled in the art would recognize that the die seal canbe passive or electrically active. On each 3D stack layer, or stratum,the electronic circuits within one die, that may be circumscribed by adicelane, may not be connected to the electronic circuits of a seconddie on that same wafer, that second die also may be circumscribed by adicelane. Further, the dicelane/scribelane of one stratum in the 3Dstack may be aligned to the dicelane/scribelane of another stratum inthe 3D stack, thus providing a direct die singulation vector for the 3Dstack of stratums/layers.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, drawings or illustrations may notshow n or p wells for clarity in illustration. Moreover, transistorchannels illustrated or discussed herein may include dopedsemiconductors, but may instead include undoped semiconductor material.Further, any transferred layer or donor substrate or wafer preparationillustrated or discussed herein may include one or more undoped regionsor layers of semiconductor material. Moreover, epitaxial regrow ofsource and drains may utilize processes such as liquid phase epitaxialregrowth or solid phase epitaxial regrowth, and may utilize flash orlaser processes to freeze dopant profiles in place and may also permitnon-equilibrium enhanced activation (superactivation). Further,transferred layer or layers may have regions of STI or other transistorelements within it or on it when transferred. Rather, the scope of theinvention includes combinations and sub-combinations of the variousfeatures described hereinabove as well as modifications and variationswhich would occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims

The invention claimed is:
 1. A 3D semiconductor device, the devicecomprising: a first level, wherein said first level comprises a firstlayer, said first layer comprising first transistors, and wherein saidfirst level comprises a second layer, said second layer comprising firstinterconnections; a second level overlaying said first level, whereinsaid second level comprises a third layer, said third layer comprisingsecond transistors, and wherein said second level comprises a fourthlayer, said fourth layer comprising second interconnections; and aplurality of connection paths, wherein said plurality of connectionpaths provides connections from a plurality of said first transistors toa plurality of said second transistors, wherein said second level isbonded to said first level, wherein said bonded comprises oxide to oxidebond regions, wherein said bonded comprises metal to metal bond regions,wherein said third layer comprises crystalline silicon, wherein saidsecond level comprise electronic circuits and at least one test circuit,and wherein said at least one test circuit is capable to perform testingof at least one of said electronic circuits.
 2. The device according toclaim 1, wherein said at least one test circuit is connected to at leastone of said connection paths.
 3. The device according to claim 1,wherein said second level comprises at least one phase-lock-loop (“PLL”)circuit.
 4. The device according to claim 1, wherein said second levelcomprises at least one charge trap circuit.
 5. The device according toclaim 1, wherein said second level comprises at least one powerregulator circuit.
 6. The device according to claim 1, wherein saidsecond level comprises at least one memory array, wherein said firstlevel comprises at least one control circuit, and wherein said at leastone control circuit controls read operations of said at least one memoryarray.
 7. The device according to claim 1, wherein said second levelcomprises at least one electronic-surge-discharge (“ESD”) circuit.
 8. A3D semiconductor device, the device comprising: a first level, whereinsaid first level comprises a first layer, said first layer comprisingfirst transistors, and wherein said first level comprises a secondlayer, said second layer comprising first interconnections; a secondlevel overlaying said first level, wherein said second level comprises athird layer, said third layer comprising second transistors, and whereinsaid second level comprises a fourth layer, said fourth layer comprisingsecond interconnections; a plurality of connection paths, wherein saidplurality of connection paths provides connections from a plurality ofsaid first transistors to a plurality of said second transistors,wherein said second level is bonded to said first level, wherein saidbonded comprises oxide to oxide bond regions, wherein said bondedcomprises metal to metal bond regions, wherein said third layercomprises crystalline silicon, wherein said second level comprises atleast one array of memory cells, wherein said memory cells are volatiletype memory cells, and wherein each of said memory cells are a singletransistor memory cell.
 9. The device according to claim 8, wherein saidfirst level comprises at least one control circuit, and wherein said atleast one control circuit controls read operations of said array ofmemory cells.
 10. The device according to claim 8, wherein said secondlevel comprises at least one phase-lock-loop (“PLL”) circuit.
 11. Thedevice according to claim 8, wherein said second level comprises atleast one charge trap circuit.
 12. The device according to claim 8,wherein said second level comprises at least one power regulatorcircuit.
 13. The device according to claim 8, wherein said second levelcomprises at least one electronic-surge-discharge (“ESD”) circuit. 14.The device according to claim 8, wherein at least one of said secondtransistors is a FinFET type transistor.
 15. A 3D semiconductor device,the device comprising: a first level, wherein said first level comprisesa first layer, said first layer comprising first transistors, andwherein said first level comprises a second layer, said second layercomprising first interconnections; a second level overlaying said firstlevel, wherein said second level comprises a third layer, said thirdlayer comprising second transistors, and wherein said second levelcomprises a fourth layer, said fourth layer comprising secondinterconnections; and a plurality of connection paths, wherein saidplurality of connection paths provides connections from a plurality ofsaid first transistors to a plurality of said second transistors,wherein said second level is bonded to said first level, wherein saidbonded comprises oxide to oxide bond regions, wherein said bondedcomprises metal to metal bond regions, wherein said second levelcomprises at least one memory array, wherein said third layer comprisescrystalline silicon, and wherein said second layer comprises radiofrequency (“RF”) type circuits.
 16. The device according to claim 15,further comprising: a heat removal path from said third level to anexternal surface of said device.
 17. The device according to claim 15,wherein said second level comprises at least one SerDes circuit.
 18. Thedevice according to claim 15, wherein said second level comprises atleast one phase-lock-loop (“PLL”) circuit.
 19. The device according toclaim 15, wherein said second level comprises at least oneelectronic-surge-discharge (“ESD”) circuit.
 20. The device according toclaim 15, wherein said second level comprises at least one powerregulator circuit.